First version of uae4arm-rpi for Gameshell ready for download. Instructions may be found here. All you need is to place action.config to /home/cpi/apps/launcher/Menu/GameShell/20_Retro\ Games/Amiga. As usual with SSH, read ssh howto if you need help. The action should then automatically download the emulator. Should the action fail to do this, you may manually download it from here, then upload the unzipped uae4arm file to Gameshell to /home/cpi/apps/emulators directory.
I did also prepare an optional launcher icon:
Example configuration files, as explained in Readme, may be found here
The emulator runs well enough for the games I want to play on Gameshell. There are a few things that could be improved in the future, if time permits.