The Witcher 3 - probably never coming

Darksiders - became so low priority since it switched hands, it's probably never coming

Rocket League - well they did say Q2, but after so many delays already who knows. It also became an obviously low priority item

Total War: Rome II - was likely replace by the more recent one Attila that was ported, in January there was no updates: https://www.gamingonlinux.com/articles/looks-like-total-war-rome-ii-might-not-be-coming-to-linux-steamos-now.6460

Witcher 3, sadly.

Witcher 3 has one chance - rewrite of the engine for enhanced edition. It's not an unheard of thing for CDPR. If they learned from past mistakes, they'll use Vulkan, and then chances of the Linux version will grow. But if EE won't happen - TW3 for Linux won't happen either. The only option will be Wine then.

Not a game necessarily but GOG Galaxy. It's been out on Windows and Mac for a while now without even an ETA for Linux. Just look at how many posts there are on their Community Wishlist for Galaxy Linux which has been in the top 5 community wishes for Galaxy for a long time.

As for actual games:

The Vanishing of Ethan Carter. Last I heard, difficulties put the port on hold. Probably by a ton of proprietary middleware.

Primal Carnage which was announced for Linux in 2009! It only made it to PS4 and Windows with dropped plans for any Linux port.

Darksiders I and II definitely. I was so hyped for it when Godlewski released the screenshots of it running in Linux. But it's what, going on three years now? No real movement in steamdb in around a year it seems. I hold out hope one day it will show up, but definitely not waiting on it. I think the Witcher 3 is more likely than Darksiders but I'm not waiting on it either. I'm following the rules and not talking about Rocket League. Project Cars is the only one I would really add to that list.

- Darksiders 1 and 2
- The Witcher 3
- Batman (but Windows gamers are not more luckyer, such a bad port)

Giana Sisters Twisted Dreams - The Humble Bundle entry saying "Giana Sisters: Twisted Dreams will be available for Mac and Linux later this year." The message has been there more or less since 2014. The last it was heard of is that the port was finished by an outside developer but it was badly broken, even had an entire level missing.

Witcher 3 - Unless they write a Vulkan API I don't see them doing an OpenGL version. They've been pretty much quite about their plans and if I had to make an optimistic guess I'd say they were waiting on Vulkan. Till the drivers for it stabilize, CDPR would begin testing the game. Unless they plan to support Linux in their future games I don't see a Linux W3 happening.

Project CARS, they don't have any reference to Linux/SteamOS in the main website and after the announce, we didn't get any news on the status of the port.

MineCraft Story Mode- Much like Rocket League, only seems to update the Windows/Mac depots any more; I don't think Telltale really care about us at this point.

Undertale- Got so fed up with waiting I just played via WINE. To it's credit, it's a very charming game, it's just a shame Toby can't be bothered to finish a port; even after grabbing Linux testers.

What a depressing thread .-.

Rocket League: it was supposed to be released earlier this year. I don't know if someone is still working on it but we had some news on it so, sooner or later it will be there.
The Witcher 3: it will be awesome but I don't expect it anymore.