> The Julia -> Metal stack is comparatively not very portable

You can do "Julia -> KernelAbstractions.jl -> Metal", "Julia -> KernelAbstractions.jl -> CUDA", etc. if you need portability. This is already used by some of the numerical libraries in the ecosystem.

Sure, you could do that for any language/SDK if you're patient enough. You could scrap the abstraction layer altogether and litter the whole thing with ifdefs if you're really lazy.

We're definitely going to see people using higher-level libraries to abstract all this away in the future though. We knew this was going to happen a decade ago, so it's been frustrating watching GPU standards fragment while featureset demands consolidate. Nowadays there is basically no upside to writing a raster program with native GPU libraries when you could target a higher-level standard with oftentimes better performance.