Quite a few months have passed since Total War: Warhammer first appeared, and if you are still waiting for the Linux port to appear I have some good news! According to a surprisingly brief announcement, the Linux version will be arriving next Tuesday, November 22! If you already own the PC version, don't worry about having to buy it twice as it will automatically be granted to you. And naturally, the same works in reverse.
As for the Mac version, that one is still in limbo. The reason for this is that the developers are waiting for an apparently important Metal update (check the link if you want a good explanation of what Metal even is), and as such the Mac version is currently on hold. On the positive side, if the same timeframe applies to Total War: Warhammer as it does for the developer's other Mac port Deus Ex: Mankind Divided, then you can expect to see the Mac version either later this year, or early next year.
And speaking of developers, this port isn't being made by Creative Assembly, but rather by an outside party. In this case its Feral Interactive, the talented folks behind the Mac and Linux ports of Mad Max, XCOM 2, Tomb Raider, Deus: Ex Mankind Divided, and so forth. Given Feral's experience porting games, as well as the generally positive reception for their previous work, I think its fairly safe to assume that Total War: Warhammer will be one of the more competent ports out there. So here's to hoping I don't end up being terribly, terribly wrong!
If you don't know much about Total War: Warhammer, you can either check out my review by heading over here, or one of Sega's videos that goes over exactly that topic. Have a look: