I think adding onto RetroPie via a script makes the most sense. It won't rub anyone the wrong way and it will also allow people using SD images (I dislike this) to try the FE.
Why not leverage the original script as a base and install the same way - "bash <(curl -s
https://bitbucket.org/teamretro/retrofe/raw/default/Scripts/Raspi2/install.sh)"? Getting built into a future release of RetroPie might be good but in the case of Attract-Mode, it's less than desirable.
I'll post a couple of the scripts that I made for my RetroPie to Attract-Mode migration with a twist to support RetroFE. They should be similar to some of the things you might want for RetroFE.
DB_From_HS.sh
wget http://hyperlist.hyperspin-fe.com/genall.php?system=311 -O "/home/pi/retrofe/meta/hyperlist/Atari 2600.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=1 -O "/home/pi/retrofe/meta/hyperlist/Atari 5200.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=31 -O "/home/pi/retrofe/meta/hyperlist/Atari 7800.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=2 -O "/home/pi/retrofe/meta/hyperlist/Atari Lynx.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=6 -O "/home/pi/retrofe/meta/hyperlist/MAME.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=16 -O "/home/pi/retrofe/meta/hyperlist/NEC TurboGrafx-16.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=44 -O "/home/pi/retrofe/meta/hyperlist/Nintendo 64.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=316 -O "/home/pi/retrofe/meta/hyperlist/Nintendo Entertainment System.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=125 -O "/home/pi/retrofe/meta/hyperlist/Nintendo Game Boy.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=35 -O "/home/pi/retrofe/meta/hyperlist/Nintendo Game Boy Advance.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=124 -O "/home/pi/retrofe/meta/hyperlist/Nintendo Game Boy Color.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=14 -O "/home/pi/retrofe/meta/hyperlist/Sega 32X.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=56 -O "/home/pi/retrofe/meta/hyperlist/Sega CD.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=48 -O "/home/pi/retrofe/meta/hyperlist/Sega Dreamcast.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=302 -O "/home/pi/retrofe/meta/hyperlist/Sega Game Gear.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=319 -O "/home/pi/retrofe/meta/hyperlist/Sega Genesis.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=308 -O "/home/pi/retrofe/meta/hyperlist/Sega Master System.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=319 -O "/home/pi/retrofe/meta/hyperlist/Sega Genesis.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=309 -O "/home/pi/retrofe/meta/hyperlist/Sony PlayStation.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=310 -O "/home/pi/retrofe/meta/hyperlist/Sony PSP.xml"
wget http://hyperlist.hyperspin-fe.com/genall.php?system=303 -O "/home/pi/retrofe/meta/hyperlist/Super Nintendo Entertainment System.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Atari 2600.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Atari 5200.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Atari 7800.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Atari Lynx.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/MAME.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/NEC TurboGrafx-16.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Nintendo 64.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Nintendo Entertainment System.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Nintendo Game Boy.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Nintendo Game Boy Advance.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Nintendo Game Boy Color.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Sega 32X.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Sega CD.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Sega Dreamcast.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Sega Game Gear.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Sega Master System.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Sega Genesis.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Sony PlayStation.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Sony PSP.xml"
attract -i "/home/pi/retrofe/meta/hyperlist/Super Nintendo Entertainment System.xml"
Menu_Plus_Setup.sh
mkdir /home/pi/RetroPie/roms/setup
cat >> /home/pi/RetroPie/roms/setup/EmulationStation.sh << EOF
clear
echo "Switching default boot system to EmulationStation and rebooting"
echo ""
sed -i 's/attract/emulationstation/g' /opt/retropie/configs/all/autostart.sh
sudo reboot
EOF
cat >> /home/pi/RetroPie/retropiemenu/Attract-Mode.sh << EOF
echo "Switching default boot system to Attract-Mode and rebooting"
echo ""
sed -i 's/emulationstation/attract/g' /opt/retropie/configs/all/autostart.sh
sudo reboot
EOF
chmod +x /home/pi/RetroPie/retropiemenu/Attract-Mode.sh
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/audiosettings.rp >> "/home/pi/RetroPie/roms/setup/Audio Settings.sh"
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/bluetooth.rp >> /home/pi/RetroPie/roms/setup/Bluetooth.sh
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/configedit.rp >> "/home/pi/RetroPie/roms/setup/Configuration Editor.sh"
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/wifi.rp >> "/home/pi/RetroPie/roms/setup/Configure Wifi.sh"
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/filemanager.rp >> "/home/pi/RetroPie/roms/setup/File Manager.sh"
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/raspiconfig.rp >> "/home/pi/RetroPie/roms/setup/Raspberry Pie Setup.sh"
echo sudo reboot >> /home/pi/RetroPie/roms/setup/Reboot.sh
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/retroarch.rp >> "/home/pi/RetroPie/roms/setup/Retroarch Setup.sh"
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/retronetplay.rp >> "/home/pi/RetroPie/roms/setup/Retroarch Netplay.sh"
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/rpsetup.rp >> "/home/pi/RetroPie/roms/setup/RetroPie Setup.sh"
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/runcommand.rp >> /home/pi/RetroPie/roms/setup/RunCommand.sh
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/showip.rp >> "/home/pi/RetroPie/roms/setup/Show IP Address.sh"
echo sudo poweroff >> /home/pi/RetroPie/roms/setup/Shutdown.sh
echo sudo /home/pi/RetroPie-Setup/retropie_packages.sh retropiemenu launch /home/pi/RetroPie/retropiemenu/splashscreen.rp >> "/home/pi/RetroPie/roms/setup/Splash Screen.sh"
mkdir /home/pi/RetroPie/roms/setup/box
mkdir /home/pi/RetroPie/roms/setup/cart
mkdir /home/pi/RetroPie/roms/setup/box
mkdir /home/pi/RetroPie/roms/setup/marquee
mkdir /home/pi/RetroPie/roms/setup/snap
mkdir /home/pi/RetroPie/roms/setup/video
mkdir /home/pi/RetroPie/roms/setup/wheel
cp /home/pi/RetroPie/retropiemenu/icons/audiosettings.png "/home/pi/RetroPie/roms/setup/snap/Audio Settings.png"
cp /home/pi/RetroPie/retropiemenu/icons/bluetooth.png /home/pi/RetroPie/roms/setup/snap/Bluetooth.png
cp /home/pi/RetroPie/retropiemenu/icons/configedit.png "/home/pi/RetroPie/roms/setup/snap/Configuration Editor.png"
cp /home/pi/RetroPie/retropiemenu/icons/wifi.png "/home/pi/RetroPie/roms/setup/snap/Configure Wifi.png"
cp /home/pi/RetroPie/retropiemenu/icons/filemanager.png "/home/pi/RetroPie/roms/setup/snap/File Manager.png"
cp /home/pi/RetroPie/retropiemenu/icons/raspiconfig.png "/home/pi/RetroPie/roms/setup/snap/Raspberry Pie Setup.png"
cp /home/pi/RetroPie/retropiemenu/icons/retroarch.png "/home/pi/RetroPie/roms/setup/snap/Retroarch Setup.png"
cp /home/pi/RetroPie/retropiemenu/icons/retronetplay.png "/home/pi/RetroPie/roms/setup/snap/Retroarch Netplay.png"
cp /home/pi/RetroPie/retropiemenu/icons/rpsetup.png "/home/pi/RetroPie/roms/setup/snap/RetroPie Setup.png"
cp /home/pi/RetroPie/retropiemenu/icons/runcommand.png /home/pi/RetroPie/roms/setup/snap/RunCommand.png
cp /home/pi/RetroPie/retropiemenu/icons/showip.png "/home/pi/RetroPie/roms/setup/snap/Show IP Address.png"
cp /home/pi/RetroPie/retropiemenu/icons/splashscreen.png "/home/pi/RetroPie/roms/setup/snap/Splash Screen.png"
chmod +x /home/pi/RetroPie/roms/setup/*.sh
wget http://attractmode.org/images/logo.png
mv logo.png /home/pi/RetroPie/retropiemenu/icons/Attract-Mode.png
cat >> /home/pi/.attract/emulators/Setup.cfg << EOF
# Generated by Attract-Mode v2.2.1
#
executable /bin/bash
args "[romfilename]"
rompath /home/pi/RetroPie/roms/setup
romext .sh
system Setup
artwork box /home/pi/RetroPie/roms/setup/box
artwork cart /home/pi/RetroPie/roms/setup/cart
artwork flyer /home/pi/RetroPie/roms/setup/box
artwork marquee /home/pi/RetroPie/roms/setup/marquee
artwork snap /home/pi/RetroPie/roms/setup/video;/home/pi/RetroPie/roms/setup/snap
artwork wheel /home/pi/RetroPie/roms/setup/wheel
EOF
sed -i '/\<sound\>/i \display Setup' /home/pi/.attract/attract.cfg
sed -i '/\<sound\>/i \ layout Basic' /home/pi/.attract/attract.cfg
sed -i '/\<sound\>/i \ romlist Setup' /home/pi/.attract/attract.cfg
sed -i '/\<sound\>/i \ in_cycle yes' /home/pi/.attract/attract.cfg
sed -i '/\<sound\>/i \ in_menu yes' /home/pi/.attract/attract.cfg
sed -i '/\<sound\>/i \ filter all' /home/pi/.attract/attract.cfg
sed -i '/\<sound\>/i \ ' /home/pi/.attract/attract.cfg
sed -i 's/window_mode default/window_mode fullscreen/g' /home/pi/.attract/attract.cfg
attract -b Setup
sed -i '/<\<gameList\>>/a \ </game>' /opt/retropie/configs/all/emulationstation/gamelists/retropie/gamelist.xml
sed -i '/<\<gameList\>>/a \ <image>./icons/Attract-Mode.png</image>' /opt/retropie/configs/all/emulationstation/gamelists/retropie/gamelist.xml
sed -i '/<\<gameList\>>/a \ <desc>Change system boot to the Attract-Mode frontend and reboot.</desc>' /opt/retropie/configs/all/emulationstation/gamelists/retropie/gamelist.xml
sed -i '/<\<gameList\>>/a \ <name>Attract-Mode</name>' /opt/retropie/configs/all/emulationstation/gamelists/retropie/gamelist.xml
sed -i '/<\<gameList\>>/a \ <path>./Attract-Mode.sh</path>' /opt/retropie/configs/all/emulationstation/gamelists/retropie/gamelist.xml
sed -i '/<\<gameList\>>/a \ <game>' /opt/retropie/configs/all/emulationstation/gamelists/retropie/gamelist.xml
sudo reboot