It seems (wasn't really that clear?) that Maya was running emulation? (as in, x64 binary). I don't think Maya's viewport on MacOS actually runs with Metal (it's still OpenGL), so I doubt it's a native port.

Did it do any CPU-intensive stuff (skinning, deformation), or was it just GPU-intensive viewing?

High-end VFX will be interesting for this with Apple (Maya, Houdini, Nuke) - already there was quite a lot of anger at OpenGL being deprecated and Vulcan not being officially supported. Another instruction set into the mix for highly-optimised apps (lots of SIMD code) is going to be quite annoying, especially for the CPU renderers (Arnold, Renderman, etc)...