It will be released when it's ready.
If Toady announces a specific date that the next release will be ready, it could be of the quality of many of the non-indy games. Specifically, Indy games tend to be somewhat better (in terms of quality per coders) because the coders don't have to work with such deadlines. Announcing a release date is the same as making a deadline. Deadlines cause stress. Stress causes programming problems, which requires debugging, which can cause more stress. In the end, you get a mess of code which may or may not actually work as intended, frequently a lower quality then what could have resulted with the exclusion of a deadline.
On the other hand, if one does "snapshot releases" (where they aren't trying to meet a deadline, but still have an announced release schedule for whatever is written then), you can end up with loads of builds which aren't really useful for playing, but more tailored for finding bugs in new code. However, because of how complicated DF's code seems to be (the 9+MB executable is _after_ heavy size optimization I surmise, taking evidence from the non-standard calling conventions used at the machine level), a good number of these builds might not even work in any meaningful way due to all the interactions, and the heavy optimization makes code debugging a pain (when I do compiles with gcc, I always `-g -O0` if I will debug). Besides, this technique pretty much only makes sense where the codebase is open, since then anyone could `-g -O0` it and then gdb it to the circus and back.
In the end, tl;dr, it is better the way it currently is, where releases are released when they are ready. Scheduled releases of any form aren't really appropriate for what Dwarf Fortress is.
EDIT: In case it isn't clear to anyone, I am a Great Programmer, but administration roles display with a greater priority