D meets GPU: recommendations?

[Bruce Carneal]

The project I've been working on for the last few months has a 
compute backend that is currently written MT+SIMD.  I would like 
to bring up a GPU variant.

If you have experience with this sort of thing, I'd love to hear 
from you, either within this forum or at beerconf.

In a past life I was a CUDA programmer, but I'd prefer to use 
something now that has at least some chance of running on most 
mobile devices in the future.

In addition to the CUDA fallback, I've looked at SycL, dcompute 
and, as suggested by Ethan a couple of beerconfs back, I looked 
in to the D/MLIR work.  That work is very nice but I didn't find 
the connection to GPUs.

Guidance from experience regarding any of the above, or other, 
GPU possibilities would be most welcome.