I wonder what changed? Are the rides too complex now that it causes things to move back so much? Just seems like all parks are now doing this. Like 4 things are opening "summer 2016" in Orlando (Soarin, Frozen, Kong, and Mako) and none of them have opening dates yet. It seems like an entire industry change because I remember HP 1 had sold packages way in advance and then couldn't make that as an opening date and had to limit the packages to work with soft openings. So since that point Uni hasn't had far in advance opening/packages either. It seems like since that point no one has had advance dates.
I don't understand it either. I would have thought with the advances in construction that attractions would be easier to build now than ever. Fair enough rides are more complex but Mako is probably no different than any other coaster unless they're planning something overly ambitious for the station and queue.
No doubt though that the level of theming has been put up a level since Harry Potter first opened but I would expect most of the time is spent in planning which shouldn't really make a difference to us from when a ride's PR release is out to the public.