If you go around a holiday, no matter which one, you can count on it being busy. When Easter is in March, it is twice as busy since Spring break and Easter week are usually togther or within the same 2 weeks period
I don't think there's any way to answer that right now...or at least until the majority of 2007-2008 school calendars come out.
In 2005 Easter was early but a good number of schools in the northeast were off for a week in mid-April, which made the parks very crowded even though Easter was in March.
While I admire your forward thinking, I'm afraid you might have to wait another 14 or 15 months for a definitive answer.
We were there 2 weeks after Easter this year, and it wasn't bad most of the time. We're hoping to go 2 weeks before Easter in 2007. I'm sure it'll be crowded, but hey -- we'll be there anyway!