Very cool project, and I love to see more work in this space.
Something else to look at is the Vortex project from Georgia Tech[1]. Rather than recapitulating the fixed-function past of GPU design, I think it looks toward the future, as it's at heart a highly parallel computer, based on RISC-V with some extensions to handle GPU workloads better. The boards it runs on are a few thousand dollars, so it's not exactly a hobbyist friendly, but it certainly is more accessible than closed, proprietary development. There's a 2.0 release that just landed a few months ago.
Something else to look at is the Vortex project from Georgia Tech[1]. Rather than recapitulating the fixed-function past of GPU design, I think it looks toward the future, as it's at heart a highly parallel computer, based on RISC-V with some extensions to handle GPU workloads better. The boards it runs on are a few thousand dollars, so it's not exactly a hobbyist friendly, but it certainly is more accessible than closed, proprietary development. There's a 2.0 release that just landed a few months ago.
[1]: https://vortex.cc.gatech.edu/