Steam sales end January 4th.

Also, you should just do what I plan to do. Wait for DOS:EE to go on super sale (which it will since it's only 33% off now and if it doesn't, pick it up on the 4th for 33% off) regardless of whether OSX/Linux are released.

After you purchase you'll still have 14 days to return to steam (which considering they're really just working on fixing 1 bug, the game will likely be released by this time).

The plan of the century