We've found the parks to be just slightly less crowded in the days leading up to the 25th than after it. Park hours last year had 9AM openings on the 24th for EC and AK (8AM at MK and 8:30 at HS), but from the 25th thru New Years Eve it was 8AM at all parks. We utilized EMH and FP's to avoid lines as much as possible. With a 7AM EMH, the parks aren't super crowded for about 3-4 hours.
The issues will be in planning. Park hours you see now (it looks like the posted hours begin at 9AM) will certainly change. And they may change multiple times. More EMH will be added - certainly at the MK (at least every day from the 24th - 31st) and likely at AK. And the additional EMH likely won't be updated until AFTER the 60 day FP booking window.
Knowing this, last year we booked early FP's (9, 10, 11 - or 8:30, 9:30, 10:30) and utilized EMH for other popular rides at all the parks. We used the posted EMH dates for EC, AK, HS - and anticipated EMH for MK.