How feasible is it for this to target earlier AMD archs down to even GFX1010, the original RDNA series aka the poorest of GPU poor?

Don't let anyone dissuade you, it's going to be annoying but it can be done. When diffusion was new and rocm was still a mess I was manually patching a lot to get a vii, 1030, then 1200 working well enough.

It's a LOT less bad than it used to be, amd deserves serious credit. Codex should be able to crush it once you get the env going