I would definitely prefer to have some of the "reformed" bad guys stay reformed, which means a few of the classic Brotherhood guys. Pyro was actively working with X-Men, even if they were calling themselves "Marauders" at the time, Blob seemed happy to just tend bar (and even Blob joining the bad guys in Uncanny Avengers was only because he thought he was following Cyclops), Avalanche tried to join the X-Men. Toad has been through a lot (and will hopefully get resurrected with everyone else at the end of Fall of X), and I just want him to actually be happy for awhile. Anyone one of these guys could turn "bad" again out of anger or bitterness at what's happened to Krakoa, but I'd rather they stay semi-good, or at least retired from super-villiany. Or at least give them some nuance if they wind up on a Brotherhood again, like a re-villianized Pyro should still hesitate to attack people like Storm, Iceman or Bishop, whom he bonded with as a Marauder. Similarly, Frenzy and Tempo should stay on the side of heroes.
I wouldn't mind seeing Fabian Cortez go bad again and lead a new Brotherhood, he's such a hilarious little weasel. There are plenty of other Acolytes or MLF members that could use some play. Anne-Marie Cortez has been dead forever, the Kleinstock Bros, Unuscione, Spoor, Dragoness, Wildside, Reaper, Thumbelina, etc. And for an actual Brotherhood alumn, Phantazia. She hasn't gotten to do anything in forever.
I could see Mystique and Destiny going either way, they are fun grey-area characters that have leaned more heroic during the Krakoa era. They might form a new Brotherhood if Destiny got a vision showing that it was necessary.
Edit - oh, and I forgot, Mastermind! He never really reformed doing the Krakoa era. Or either of the two Mastermind sisters (or both).