Tripwire has announced the final release date for Killing Floor 2 on November 18th. They have also said that Linux files will come post launch.
The good news is their wording implies they are actively working on it in some form.
I really liked the first Killing Floor, but the Linux release still has some issues that were never fixed which is sad. Hopefully with them doing it in-house this time they pay more attention to the Linux version.
About the game (Official description)
Killing Floor 2 is the successor to the ridiculously fun and successful original title, that was released in 2009. We released Killing Floor 2 on Steam via Early Access in April 2015 and over the last 7 months have rolled out 3 massive content updates as we get closer and closer to the final release.
In KILLING FLOOR 2 players descend into continental Europe where the outbreak caused by Horzine Biotech’s failed experiment has quickly spread and gained unstoppable momentum, essentially paralyzing the European Union. Just one month after the conclusion of the events in the original KILLING FLOOR, the specimen clones are everywhere and civilization is in disarray; communications have failed, governments have collapsed, and military forces have been systematically eradicated. The people of Europe know survival and self-preservation too well and lucky survivors have gone into hiding.
Not all have given up hope though... A group of civilians and mercenaries have banded together, paid for by Horzine, to combat the outbreak and established privately funded operation bases across Europe. Upon tracking specimen clone outbreaks, players will descend into zed-laden hot zones and exterminate them.