I have a traumatic experience with GPU-based GUI. Long time ago I tried to run Ubuntu in a VM, and they switched to GPU-based rendering. But as VM doesn't have a GPU, the system fell back to something called "llvmpipe". The result was that the widgets reacted approximately with 30 second lag to every action.

So what I am asking, if you are making a GPU-based rendering toolkit, please write also SIMD software fallback without shaders. Remember how fast Windows 95 was and make it a little bit faster.