Shen’s Last Gift is the next DLC available for XCOM 2 that brings in mech units to help you fight the alien menace.
They didn't mention Linux/Mac in the press release, but their official website states this:
QuotePlease note: Mac and Linux versions are coming soon.
Going by the delay on the last DLC release, we're looking like it could be 1-2 weeks for Feral to catch up and release it.
I will have much more to say about it when it's released and I've had a play with it, sounds like fun though compared to the last DLC!