TBH I would say in the case of the watch, it's held back much more by energy budgets than software; the software is just enforcing that. It's cute that you can run Quake on it, but for how long before it killed the battery? 20 mins? You can see Apple pushing the bounds of what it can get away with and still maintain acceptable battery life from generation to generation.
Yeah you can’t directly use Metal or MetalKit on the watch, so you can’t do completely custom rendering of anything in the GPU (which is why this port has to use software rendering), but even if you could would probably just be blowing through the battery in under an hour.
SceneKit is available. Not sure what the battery life is like when it’s used for anything other than displaying a simple 3D model briefly (e.g. like the fitness medals).
