The price of the MV will keep newbies and families from booking an MV. The Dream MV was pretty much kid free and mostly Golds/Plats cruising. We did a Dream B2B on the MV and the following cruise was SO much different in cruisers. I bet the kid/newbie ratio jumped to like 50%.
I would expect almost the same for the Fantasy MV but the next cruise (the old MV date) kept the same high price so, i wouldn't expect more kids/newbies until the 3rd/4th cruise.
I agree that overall I think there will be less kids than a normal cruise, but I think there will be many more than were on the Dream maiden voyage, only because this one is going to fall on several spring breaks. The Dream's maiden voyage was late January and most kids were stuck in school.
I also agree that the total passenger count will be closer to 3000 people than 4000.