[Derpdiherp]

To be honest I think Tarn isn't wanting to release the source for a couple of reasons:

A - He wants complete control of the direction that the game is heading,

B - He's not proud of the source code, from interviews and such and the length of the project I think it's rather a mess, and due to the fact that the game gets new features all the time, it's not getting refactored any time soon.

In a way it's a shame - the dwarf fortress community has been fighting "FPS death" of fortresses, when the simulation of all the stuff on your fortress reaches the point where the game crawls along so slowly it's unplayable. And this happens sooner than you'd think. People have been pushing to get the game multithreaded for years but unfortunately it's just not happening. Yet on the other hand I respect Tarns decision to want complete control over the direction of the game - yet there are already mods out there that completely change that anyway.