I am in turmoil thinking about this because thinking about the last two seasons, BB14 without Dan, Britney, Boogie and Janelle, and BB13 without Brenchal, Jeff, Jordan, Dick and Danielle is kind of unimaginable. Without these characters I don't think either series would have been as good. And when you look at BB12 which was the last series without any returning players it was a really bad series.
In saying that BB13 was too unbalanced as there were too many vets around to run things, without Danielle around to start a war it would have been very dull watching all the newbies get picked off one by one. BB14 worked a bit better since the vets were forced to work alongside the newbies. If they are bringing people back I think it should be no more than 4 players or all newbies. It's probably too soon for another Allstars.