How anxious are you to test it? I can try to make a module of https://github.com/libretro/beetle-psx-libretro which is a port of the mednafen emulator you speak of. Can’t guarantee the performance as the current one is optimised for arm, this may not be.
As far as the prelaunch video instead of an image, you’d have to recode runcommand to call omxplayer and your video. I doubt we’ll integrate video support for runcommand, likely something like that will just have to be done manually.