There are missing features for older versions too:
- bufferRobustness2 - geometry shaders - transform feedback - tessellation is super but very slow and problematic
Geometry shaders and transform feedback are terrible features that most GPU vendors would like to get rid of because they don't map well to modern hardware. But games do use them and everyone who isn't Apple has to maintain backwards compatibility. So it's unlikely that those will ever get supported in Metal. You could probably emulate them with varying levels of compatibility/conformance which might be good enough for a lot of games.