Tate and Liza gave you your 7th badge. Hardly introducing the concept when we'd already had enough double battles with random trainers.A collection of pretty interesting posts from Pokebeach:
I agree with both posts quoted above. It would make sense for them to have two starters in back to back gens that have a reference to the same thing. They might clash in the anime.
The three brothers thing makes me think that it will be a triple battle for the gym badge. It would be a great way to introduce the concept, just like the double battle gym in Hoenn.
Mijumaru and its first form are Sea Otters and then they turn into a Giant Otter (actual species) with a bunch of shells on its body.