2M Chipram expansions will generally work, it's just one special type that uses the A3000 2M Agnus (8372B) that I can't test here for lack of equipment. However, the community is quick: I already have a reliable tester who offered to take his (rather special) 2M chipram expansion out of his CDTV and put it into an A500 for testing, so this will also be covered.
Another thing that will "generally work" is trapdoor memory expansions (even the larger ones with up to 1.8M using a Gary-adapter), and the more sophisticated ones with Gary-adapter and CPU-adapter for added chipram with 1M Agnus.
Flickerfixers (internal, external and mixed internal/external models) will also work with the ACA500. Only things that will conflict are the ones that go on the CPU port (side port) or the CPU socket.