"How many years will it take to get a reliable Go or Rust support for programming a vendor-independent GPU? What's the overhead compared to say C or C++?"
We're already using Rust for OpenGL ES 2.0-based graphics programming.
I didn't expect that, I am almost surprised! Though, I was more after using Rust or Go for general purpose GPU computing via OpenCL for example. There seems to be some form of project for binding, but I certainly would not put my money on some random person doing the bindings. Very experimental and unreliable stuff.
We're already using Rust for OpenGL ES 2.0-based graphics programming.