Ok I am going to answer with what I think will happen... pure speculation on my part.
Will the Leaky Cauldron be a full service restaurant or will it be similar to Three Broomsticks' counter service? I think that UO needs a full service HP restaurant. However this would put it right next to Lombard's. I don't see Lombard's going away, but I would like to see dining options expanded at both UO and IOA.
Will even more themed merchandise be created, such as items found in the Weasleys' Wizard Wheezes store? I think this is most deffinately a YES. I think you look at guest spending numbers and you see how people just eat up the HP merchandise. I think UO wants to continue to give a people to come here and spend lots of money.
How do you think crowd flow will be as this layout shoves people into a corner of the park with one area for an entrance and exit? I think if this layout is correct, you will be able to bypass the land by sticking to the boardwalk area, alleviating the need that IOA has for that temporary bridge.
Will the storyline of Gringotts is involve/mention Harry as Radcliffe has claimed not to return for more taping? I think Gringots will focus more on the world of HP and not the fact that HP is there. So I think we "muggles" might have inherited a wizards fortune and that we need to claim it.
Other than peanut butter and strawberry, what other flavors are mentioned/possible for Florean Fortescue's Ice Cream Parlour? I would love to see the Every Flavored Beans incorporated into an Ice Cream... would make for a delicious/hilarious eating experience.
Will Butterbeer be served in the exact same style of cart it is in WWOHP or will the design change? I would like to see them change it up. Since we are in London/Diagon Alley Kings Cross I would like to see it served in a more "city esq" way
What nods to films 5-8 will be present in the expansion? I honestly don't know unless Gringots will reference it.
What will the physical entrance to Leaky Cauldron/Diagon Alley be? I think this just might similar to WWOHP as it is right now. I just can't think of a way to do something clever without creating MAJOR bottle necks
Will there be a London facade shielding the land's view from the Studios? I think London will be along the BoardWalk and then you you transition into the HP areas.
What structure (if any) will take the place of the lagoon-facing buildings in Amity? I think all the Lagoon facing area will be classic London facades... Brownstone looking buildings etc
Since the midway games in Amity were replaced by temporary ones by Simpsons, what will be their final location? I want to see them take up permanent residence over at the Simpson's with Simpson's theming
What time will the Gringotts attraction clock in at? As far as attraction length? My guess is that they are going to do the 1 hour queue attraction set up with the ride clocking in at 2 - 3 minutes. It seems this one might physically move faster than FJ and because of that I think we can expect it to be shorter time wise.
It seems that Nathans was the only Amity building not demolished. Will its kitchen become retooled for the Leaky Cauldron? I think it is too soon to say that Nathans will or won't be demolished. It just hasn't been demolished yet, along with a lot of other Amity buildings.
What retail stores from the books are more likely to be realized as actual stores and which will become simple facades? The Weazleys is a big one, then a higher capacity Olivander's
We know that Gringotts will anchor the expansion, but what other shows/attractions will be created for the area? A C-ticket? MORE STREETMOSPHERE! PLEASE! I want Wizards and Witches everywhere, interacting, casting spells, making magic! But I would also love to see a Wizards duel, and of course the Hogwarts Express train from London to Hogsmede.
Would Uni start construction without telling people what it will be? And how long until they confirm what is happening? Universal is going to wait as long as possible before announcing it. Once they announce it people will delay their trips so they can come "when it is is all finished" a perfect example of this is how I personally have delayed my trip to Disneyland until DCA is "finished" I will be going in late summer. I didn't go last year when WOC opened because I wanted to wait until it was all done. Just like when they announced the WWOHP people delayed their trips to Universal. They want to wait as long as possible. construction will be well underway before any announcement is made.