Sad news, as it seems there's just no chance of Killing Floor 2 coming to Linux any more as Tripwire can't find a developer.
Going back to February of last year, Knockout Games sneaked out before that they were working on it, but not all contracts work out of course. I assumed they had parted ways, since later in August of last year Tripwire then said it wasn't in active development. I was hoping Knockout Games (or anyone) was just quietly working on it, but I guess not.
Here's what Tripwire have now said about it:
Currently all progress on a Linux Client is indefinitely on hold. While progress was made towards getting the game client to run on the platform, we have been unable to find a person or persons to finish the work needed to make a client.
The major bottleneck has been getting the rendering system up and running (the key part of the client) as the engine now works on platform (the server is the engine minus a client and loading assets it doesn't need to render/trigger). During Killing Floor 2's development a choice was made to rewrite the DirectX rendering system. This in turn means many of the "turn key" Unreal porting solutions that existed do not apply to Killing Floor 2, as they all assume that the game is using the default Unreal 3 rendering pipeline.
So far the third parties we have talked to either do not want to undertake the creation of a new OpenGL rendering pipeline from the ground up (due to time and effort involved) or have quoted a price that makes it beyond consideration (the cost versus estimated return math does not come even close to making sense based on previous Killing Floor 1 Linux sales when charted against Killing Floor 2).
If that changes, we will be happy to re-open development of a Linux client, but until that point it is on hold.
I was really looking forward to playing Killing Floor 2 one day, but it seems like it's not going to happen. Thankfully we have a lot of other great games, but it still stings a bit to hear this.
It's genuinely sad that a developer has again locked themselves into one single closed API. The annoying thing, is that they're using the sales of the original in their considerations of Linux being worth it or not for the new game. This is after previously confirming they will do it, multiple times. The problem I have with that, is Killing Floor was released for Windows in early 2009 and released for Linux in late 2012, that's well over three years after the original release when many people will have already owned it. Heck, even I already owned it, as I knew many people already did. This is part of the problem with Linux versions coming late—you will lose sales and then you will look at it like Linux sells even less than expected.
Thankfully, with game engines now having better support for OpenGL (and Vulkan support is slowly getting better), this is less of a problem for newer games—if they use an up to date version that is.
I still hope one day either someone like Ryan "Icculus" Gordon or another Linux porting champion can take another look, but considering how much work they've made for themselves, it doesn't sound likely.