I'm predicting a summer launch, possibly a WWDC announcement.
I think this will happen for a few reasons. First of all the October update was such a minor update, that I don't think Apple would wait an entire year to update again (but they also couldn't stick to the normal March timeframe, because they would only piss off more people. Just a sidenote). Secondly, the iPad mini has completely stolen the light from the full iPad. It's newer, cheaper, lighter, and more portable. The large iPad needs to regain some of its "sheen", and it will NOT be able to do that if it shares a stage with a retina mini (what everybody has been waiting for). So the full iPad will launch about 3-4 months ahead of the retina mini. This will gain it a lot of attention. Sales for the full iPad will go through the roof (it's so light! so small! so thin! it's the perfect iPad!!!), while iPad mini sales will diminish thanks to nearing the end of it's life. Then the retina mini will hit a few months later.
It's better for Apple to alternate product launches a bit. Keeps the attention on Apple.