I think that while sunset adds to the EG Humane 6, Starlight balances out the mane 6 and so the balance is even on both ends. I would, as I'm sure the other people commenting on this picture would like to see the scale tip either way for the Mane 8 to come to fruition, either in Equestria Girls or in ponyville. I'd like to see what sunset will decide to do in the future, because I'm sure, in her rush to leave with the crown, there's another book that she could have left behind or some other small detail or oversight that she would have forgotten about. I think we can all agree that we cannot prepare for every situation and there may, or may not be a situation that arises that would require travel between both worlds, whether for pony starlight or sunset. I eagerly await to see what becomes of this, and whether there will be more characters that are added to the ever-growing reality that may or may not come to fruition.