I've long wondered about using a Rasberry Pi inside a real Amiga as an assistance board for printing or something.
Actually running everything on it would resolve all the issues!
But once the its working... unless I'm doing some GPIO work, then grab the fastest ARM SBC around and get it working :-)
Rockchip 3399 is very fast chip and they are something like $20 per chip. Very good graphics. It might work well with 2 cores doing AGA / planer emulation working with the other 2d and 3d hardware on board that chip.