Is it mentioned that its connected with a subway? Its connected with the school with a bridge and a tunnel, but the school seens to be just floating in the midle of the ocean. If its connected with the mainland with a subway, i hope they some day give us a Unova subway pass to visit unova. Well, im quite sure they would actually SELL this Unova subway in form of another dlc. They could release this dlc together with the bw remakes.Just a copy, the Terarium is connected to the mainland with a subway. Unova and all of its cities are still there. Some characters mention locations/visits. It's also called 'Chargestone Cavern' instead of 'Cave'.
I wouldn't mind a flooded/post-natural disaster setting in an alternate reality sometime in a future entry, though.
BW remakes could cover the story until the time of BW2, but through the eyes of Hilbert/Hilda for the whole time. Explain why Unova was suddenly invaded by pokemon that didnt live there before. Maybe team plasma actually convinced too many people to release their pokemon, and many werent native of Unova. Too many species suddenly appearing that way is enough to cause a disarter in the ecossystem. Reshiram is also said to make the atmosfere warmer. Unova could start to flood , and the dome of the terarium might start to be built to prevent Unova from being fully flooded. Maybe Unova isnt fully covered in water, but the dome is used to cover some flooded areas, and later used by blueberry academy. This could also give us an in universe explanation to why people arent allowed to bring pokemon that arent native of Unova to Unova, or to other regions nowadays. You could visit blueberry academy in both BW remakes and S/V DLC, and people with remakes could play co -op with people with DLC.