I have read through this topic and I quite agree with many of the posts.
While a lot of us like those noisy big old retrocomputers you have to face it there is an increasing demand from the retro community and literally no supply for parts so sooner or later you will not be able to get a 6600 or a Voodoo 1/2/3. There is not enough demand to have 3DFX reopen again 😀 These 20-30 year old components going to die sooner or later and next to recapping them or reflowing them in the oven and hoping it will work there is not much more you can do at home.
I was also entertained by the thought of using KVMs PCI passthrough but for different setup to build some crazy 64 core ryzen with RTX30xx to be my main Linux workstation and run Win7 or 10 with PCI passthrough for gaming so I have a gaming+working computer in one. The only reason I use microsoft's OSes is just for gaming. I never particularly liked wine on linux because maybe 1-2 games work millions of others are broken so I dedicate like 1 hour per year trying out the latest wine release but don't have high hopes.
I think what we need is not really a passthrough but to have actual work on the 3D acceleration and OpenGL drivers for VMs. I mean an RTX3080 is more than equipped to do the work of a Voodoo3 or 6600 even with some sort of translation... For example here is 1 of my retro Vmware machines:
This runs any 2D retro games from the 99 era fine like Sc1, Diablo but of course there is no 3D acceleration. I have a similar Vmware VM with DOS/WFW311 and that's also so-so good (small issues with vmwares SB16 emulation sometimes). I was reading through the Vmware forum what happened with this 3D because I recalled them having it in some of their workstation products and they removed it because it was buggy, too hard, unfixable whatever. Seems like they gave up with it.