Its not the release date. The last couple weeks that date popped up on a store website and went from rumor to bona fide fact in record time (and thats saying something, considering that the Internet has redefined what "viral" means)
The Law of the Internet states that "rumor, oft repeated, becomes fact". At some point people assume that it's the people making the software doing the talking. Ubisoft is saying and has said nothing since October. So the target is still Q2 of 2014, which means April, May, or June. Also, March 21 is a Friday. Most games are released on Tuesday.
My prediction is the 2nd week of June. But if they REALLY had to start over to measure up to GTA V, we could be looking at lateb2014