It has came to my attention that Duke Nukem 3D: Atomic Edition & Shadow Warrior are in testing for release on Steam.
After doing further research on the steam ids it is not sure if they are ports or not but but that is yet to be discovered. Valve is testing them under ValveTestApp225140 & ValveTestApp225160. Also it seems there is a bundle planned that contains both games under Duke Nukem 3D and Shadow Warrior.
Not much is known other than the info from the Game Hub pages and exposed from Content Description Record. I will let you know as more info is known or when they are released.