Is it a good sign that mac OS is listed here? Maybe they are already playing on mac? The normal steam page still doesn't show anything about mac.
https://steamdb.info/app/289070/
"This site is not affiliated with Valve, Steam"
So I'm guessing their info is based on the fact that a Mac version was announced, and nothing more official than that. Then again a Linux version was also announced and it's not on that site...
I'd wait for the info to show up officially before getting my hopes up about anything.