This could be totally off base, but since its all speculation anyway, what the hey. Is it possible they could make it so that you can only access the portion of the Wizarding World for the park that you are in, and then if you want to board the train over to the other park you have to show your "train ticket" aka put your ticket through and have it verified as a hopper? That would solve the logistics of having the parks connected and still have it be somewhat in theme.
All that said, I would love this a lot more if I thought I could talk my Bf into going back. He doesn't do well in large crowds, so a lot of the shops were a no go and he just wanted out of the whole area. I doubt he'd want to experience a newer version that could very well be just as/more crowded since its new.