[slavik81]

Why would it be too late for something SPIR-based? Vulkan and OpenCL 2.1 will be compiling to SPIR-V.

[pjmlp]

Existing code bases and knowledge with the current tools.

You will need C++ and Fortran compilers able to target SPIR with the same set of language features, debugging tools and libraries that CUDA has available today.