Hello, I'm a returning account from a few years ago. I lost my old password, so I made a new account. I've been watching the forum for a while and I thought I'd give my thoughts on some of the discussion
First off, when it comes to the Gringott's situation I had a possible idea. What is Lego was to release a Gringott's set for around $100 which just the exterior for a year 1 and 2 set, but also released an additional set for with the vaults and dragon for about $60? I was thinking something like Jabba's Palace and the Rancour Pit from back in 2012/2013. This way we could get more Goblins, but also exciting variants of the Trio in the vaults set. I could imagine the exterior of the vaults set to have stairs that lead up to Gringott's. This way it wouldn't look completely odd. The back of the big Gringott's set could have an empty space for the mine cart system to fill in. I'd also imagine the roof of Gringott's could be removable to combine it with the Dragon from the vaults set.
Next, I'd like to give my input for Diagon Alley set. From what we've heard I imagine each building to be 2-3 floors each. The way I imagine the system working would be like the 2010/2011 Hogwarts sets with those types of connectors. However, I imagine each connector being on an 6 by 8 plate and lining up with the roofs. I think that each of these would have a unique feature to them. For example one could have a Window facade for the "magical creatures" segment of the alley so it doesn't have to have a bunch of side builds lying around. I think another one of these could have open archway with the Knockturn Alley stickers implying more buildings that way. For the entrance I imagine it being on an 8x16 plate with pin connectors on each side. This way you are able to rearrange the buildings on both sides of the alley.
As far as play features go I'd like to see some explosions in Olivanders, aswell as a moving latter feature. It'd also be nice to have the glass outside of his shop disappear but is not necessary. I can't wait to the hat reveler for WWW. I'd also like to see the Flu Powder network in one of the segments I talked about above. It'd be really cool if they included a green light brick for it as well. As far as interiors go I don't expect much for less iconic buildings. However I imagine WWW, F&B, QQS, and Olivanders are going to have packed interiors. I also hope we get a bit of the sidewalk, but I won't get my hops up.
Finally I'd like to give my input on the figures. As far a 350-400$ set goes I think 18 figures is probably what we will be seeing. We got 12 figures in the original so I do not see why 18 would be a huge stretch. My guesses are: PS Harry, COS Ron, COS Hermione, COS Draco, COS Ginny, COS Molly, COS Arthur, Lucius, Lockheart, Rita Skeeter, Fred, George, Olivander, Florean, Hagrid, Greyback, and possibly 2 death eaters. If Lego was willing to reach for 24 figures, I'd expect year 3 or year 6 versions of the trio (does not matter to me), as well as possibly Bellatrix, and maybe Ravenclaw and Hufflepuff Quidtich Mannequins.
Anyways I hope y'all enjoyed reading through some of my ideas and predictions.