I think no, you leady can play with six Players in the second edition.If they produce an expansion, it will be small, as example the Dance With Dragons expansion, or Print on Demand expansion.
I mean, what would be in such a big expansion?In the first edition,you only can with 4 Players, without the expansions, with expansions with 6 players.
New houses would be an idea, but the only house who could be in an expansion is Targaryen.But then you need another big map with Daenaerys in essos.(the bigger continent next to westeros)
And Tully and Arryn would not have much space in riverrun and in the eyrie.
So i would not expect an big expansion.