Pretty sure he said that the next specialty set would be made up of characters we've already seen. This doesn't totally rule out the Brotherhood, as such. But it means no Toad or Mastermind from the original line-up, and no Pyro, Blob, Avalanche, Destiny etc... from the Freedom Force days.You could, i guess, have a Brotherhood set with Magneto, Mystique, Scarlet Witch & Quicksilver - but that wouldn't be accurate to any particular period & DST/AA are usually pretty good about keeping their sets accurate to a certain period.
Well, we have seen Blob, albeit not the 616 version.