http://archive.is/kGoX7

When asked about a Linux version, a developer said they are "still working on it" and is "actively being worked on".

This was in April of 2015.

Update - 2016-08-15:
Tripwire said on Twitter that Linux files will come post launch.

http://archive.is/IS4My

Update - 2016-11-21
Tripwire informed Liam of GamingOnLinux that they need a developer to continue with the Linux port.

http://archive.is/9tkRv

If nothing is announced by May 21, 2017 I will add this to the curator list.

UPDATE: GamingOnLinux reported that the Linux port of KF2 is being done by Knockout Games.

http://archive.is/U5GKX

The tweet that was quoted no longer exists, so we do not have confirmation. But, I trust GoL that it's accurate.