For the A3000 and A4000 you can get something called a Prometheus board. Latest is the Firebird Prometheus. I have 2 of these from Hese which are revision 1.0 and 1.1.
As for PPC PCI. Then yes this is already a thing on Amigas thanks to the sonnet library which is being updated and can be found over in the EAB forum. I have an Apocalypse PCI PPC setup.
