hmm... well, we have stage two legendaries now... maybe we'll have stage two starters! (as in you start with the stage two.)
we have 2-pokemon-on-a-card-cards again now... maybe we'll get two starter pokemon!
they misdirected us when the first hints of the solaego and lunala cards were revealed so we wouldn't notice they hid the stage two designation... maybe the 3 pokeballs are a red herring too, and there will be four starters to choose from!
or maybe we'll get a legendary starter, or as an evolved form of the starter! or you could have a legendary pokemon only if you catch all three starters!
Theorizing is fun.