A fair question. One that made me..albeit think.
Thought about it all tonight even. And with guesstimates thanks in part to PotterVR's theater guess of 12 (as I will for the moment), I throw in a quandry (And I'd love it if I was corrected and proven wrong. Genuinely, going mathematicist here).
So let's assume in this scenario, PotterVR is primarly following suit of Fallon's example, of using lobbies as holding pens. Have an initial starting hold pen, but after that, you have three separated lobbies, each specifically made for the sake of keeping people contained for a preshow on each distinguished floor. Now let's assume it'd be 9 theaters per floor, or nine rooms per floor, where you have people experience it. For each floor having nine rooms total for when the "Ride" begins, that could allow Universal Studios Hollywood to have over 27 rooms for a Hollywood Potter VR. Perhaps more, if the motion bases are small enough to not be overly big (but I am keeping in mind distancing for each person with the interactivity of each film).
That in result, could allow if all rooms at the same time are to be used, and this is where I am probably extremely off kilter, having a capacity at around that of 324 people at that same instance.
Simpsons, does something similar; albeit with more capacity as it is done in one theater but with a gradually increased amount of vehicles in the room (being around that of 3 on the lower, 4 on the mid, and 5 on the upper). PotterVR would essentially be that for Hollywood, minus the increase per floor.
This, might be a better answer with more explanation on how they could fit in a reworked FJ overflow as-well. Assuming it shares with PotterVR in a sense.
View attachment 15699
Light Blue = Reworked FJ queue, with potential additional queue space for PotterVR West
Yellow = New Locker Location
Magenta = Main PotterVR queue, and ramps or stairs to lead people into the main lobby and preshow (With the white box as the main lobby for each floor)
Lime Green = Main brain of the area (With the main preshow and gearing up area in the large oval, with the smaller circles being that of each specific room for each specific floor)
Orange = Gift Shop
I probably screwed up, I am going to be shocked if I didn't, but this feels like to me, the ideal way to expand Hogsmeade and use PotterVR, without having to do Castle Theater nor Springfield. Let them be their own things, dangit. And yeah, as I said, I am more than excited to be wrong, as I wanna see where Universal goes from here considering how nutty Pets is in the grand scope of things.