Unofficially, there may be some people using Hackitoshs with rather beefy GPUs for machine learning.
There's a lot you can do easily on a $500 GPU that should take too long on CPU. And I prefer the shorter write/run/debug loop of working locally. It's the same niche other machine learning workstations fill, only with the preferred desktop OS.
There will also be external GPUs for Macs soon(ish), and those would be perfect for tensorflow. I'm not sure at that point they'll want it running on Macs again, and discontinuing support now may be the wrong decision.