I would be willing to guess we won't see Naxx probably til mid-June or July. They're probably about 2 weeks away from putting 1.11 on the PTR for testing, and a patch this big is going to need be tested for a good long while. How long was the PTR up for the AQ patch? Figure at least as long for this one.
Thank God. My only goal in a raiding guild is to get one dungeon on farm status before the next one is released. If you think it won't be till June or July, that shouldn't be a problem.