With how AVX512 is implemented, there isn't much point in a compiler auto optimizing general purpose code to use it, because even if there is a theoretical speedup, it may well be slower in practice.
No. I recently could really, really have used the packed saturated integer arithmetic and horizontal addition in AVX2 (but my old machine doesn't support it) and even better, the same but 512 bits wide on AVX512. It would only have been 6 or 7 instructions, if that, but it was inner loop, and mattered. Using compiler intrinsics would have been fine. I think you're looking at things too narrowly.
Actually we already have openmp to cuda (http://www2.engr.arizona.edu/~ece569a/Readings/GPU_Papers/3....) so just making it more production-ready would be perfect.
I think you got this backwards - the lack of developers' interest is what leads to the mistaken impression that GPU compute is only good for multimedia and FP-crunching workloads. Even looking at the success of GPU compute in mining cryptocoins (only ASIC's do better) ought to be enough to tell you that we could do a lot more with them if we cared to.
Because outside artificial intelligence, graphics and audio, there is little else that common applications would use the GPGPU for, so the large majority of software developers keeps ignoring heterogeneous programming models.