Well, they are too busy deciding if they should attack the Inhumans or not to care about picking a side.
I think that NewMutant was talking about not being involved in the Avengers feud.
Well, i think that she is missing because it would be a huge spoiler instead. Probably she starts in one team and ends in the other.
I would prefer that they stayed out of this, so they wouldnt be trashed like in AvX and AXIS.
50/13 years of traumas related to superheroing would cause that.