They won't want another James, Matt, Ben....they might possibly accept a young winner like Joe or Shayne. Or, as the poster above says, a young r'n'b male. I can only remember one before - Nicholas (series 2)?
They will be launching Louisa, so won't want a girl winning.
They certainly won't want another Over I don't think
But yes, another Boyband might be tried out. Either one already made (like Eton Road) or one put together (1D, Futureproof). But I think they will stick with the tried and tested four or five members.
They tried another JLS in Rough Copy, but it didn't work out.