I think you should only be able to switch characters at a landmark, landmarks are like checkpoints only you have to go there in order: save game, switch characters, etc. when are you gonna get a profile picture?
HEY! all the pokemon games were long and they were an RPG! so it goes on forever and it was also a game where you can run around and do nothing going to random cities and all that. the game can be bigger than fable extended edition! WHO KNOWS! just because it is a DS game doesn't mean that it can't be really long!