One downside I see--that is, for Nintendo, as they don't seem to fully endorse these kind of stuff--with having multiple save files is us being able to get a hold of all starter Pokémon by our own selves (in the past, we were required to have two handheld systems for this, but not that Bank exists, this is no longer the case). Even without access to multiple saves, some of us still find ourselves doing it by erasing our old file and creating a new one, but things would become much, much more easy in this regard if this feature did make it into the games.