One of my old friends from back at Assembler was doing something kind of in that realm. His name is Electronash and he and a friend FULLY reverse engineered the DC motherboard and had mapped out every single pin out and motherboard trace and whipped it up in a computer program ready to make their own DC motherboard replacements with some extra additions. They were talking about theoretically doubling the ram but this was before the double memory mod was actually a thing. Brand new SH4 MMU's can still be bought today by a company still manufacturing them from what I saw.
Some company bought the rights to them so they were pumping them out for certain customers. But he said those should work on his new board since there would be no need to cannibalize existing machines for the chipsets as many could still be purchased from 3rd party vendors. Maybe the GDRom board could be reused from a donor system but from what he said the mainboard stuff could be done for most part. He even mentioned theoretically shrinking down the board itself to have more room in the case or just making a more compact Dreamcast.
But he had a lot of stuff come up like moving a few years ago and it really put a damper on his plans. Also this pandemic was a friend to nobody so that affected things as well.
You can see his Github and Youtube here. Seems he is heavily into the MiSTer FPGA System as of late. So if anybody could do something similar it is he.
https://github.com/ElectronAshhttps://www.youtube.com/user/electronash/videosI just tweeted at him here asking what is up. He discussed this project like 5 years back and I am interested in hearing if he will do anything with the idea. He talked more updated SH4 processors with faster clock speeds even, but no idea if even feasable.
https://twitter.com/Anthony_817/status/ ... 1375039492