I suspect that generating textures directly in UV space is a bit of a dead end because UV maps are object-specific, so flux/SD/etc are going to have a hard time understanding the inputs.

I've been experimenting with image-to-image (and video-to-video) for basic texture projection, which I think shows promise:

https://bsky.app/profile/nickfisherau.bsky.social/post/3lqrl...

I just started diving into this today too:

https://github.com/YixunLiang/UniTEX

which works with in "volumetric space" (for lack of a better word), which I think makes a lot more sense.