In Kalos we had Lumoise City, and Castelia was Unova's hot spot. This makes me wonder, how will such a city be incorporated in these remakes, if at all? I really like these huge cities, as I feel it just gives Pokemon that little push towards reality that wasn't present in games before. The problem for OR/AS is that when the region was originally designed, a massive 3d city wasn't in mind. I think there are 3 ways they could handle this issue.
1. Ignore it completely. If they don't decide to develop a large central hub like city, we can't really complain, as these are remakes, and that kind of city was not present in RSE.
2. Create a new city. This could be an easier way to solve this problem, however it would still require some thinking. Game Freak would have to locate an area in which it could be built, and then design it carefully to fit in with the rest of the region.
3. Develop and alter an existing city. I personally think that this option is most likely to occur, whether it is the best option is debatable. I think the best candidates would be Slateport or Lilycove city, just because they are already the two biggest cities in the region.
Anyway, I really hope they incorporate a large city as I'd love to visit it!