Just put a PCI slot extension on the CPU card. Nice to dream......
PCI is a lot harder to interface to a 68K than most people realize.
The PT68K4 and PT68K5 boards I was using in the 80s and 90s had ISA slots which are much easier to connect to the 68K bus, but the cards available for that are more primitive.
I have two PCI bridge chips in my parts bins that are suited for use with 68K 040, 060, and earlier PPC cpus. They are still available, but they are quite complex and have some serious software requirements.
I spent a really long time considering building a system using those bridge chips, before desiding that the complexity of the needed design and the lack of decent 040 cpus made it too difficult to bother with considering the alternatives.
The last time I invested that much energy in something, I spent several months reworking a Freescale design to exchange the ALi Northbridge for a more common ATI SB600. While I was in the process of doing the board layouts, the MorphOS team released support for Mac PPC systems. As those ran just as fast or faster than what I was working on, it made continuing rather pointless.
Looking at what Jens has been talking about, makes me think we may soon be experiencing something similar.
What if instead of adding on to your A2000, you could just replace the board and have an 020/030 cpu and AGA graphics, with more memory, and maybe even a few PCI slots?