Estimated release dates are very, very tricky. On the one hand, people pledging want to know when the game will be released. On the other hand, I don't think a single Kickstarter project (or any game still in alpha development) managed to state accurately the release date of it. Development is a long and difficult process, full of surprises, and trying to guess when the game will be ready is just downright impossible. A game in development never was released before the estimated released date. It's a futile exercice, really.
Blizzard is probably one of the only developper which gets it right: "We'll release it when it's ready" (I've been quite disappointed in Blizzard lately, but at least I think they have the best approach about release dates).
It is best to avoid making promises altogether, because if you begin to make some but can't keep them, and do it multiple times, people will feel betrayed, and slowly but surely lose interest, because they will feel the developper in question can't be trusted (this apply for pretty much every situation, in fact).
So, I'll be in the "Take however long you want" camp. Just keep us informed every once in a while about the status of your game please (so far, I would say you did a good job on that part).