We've already had a number of hints as to new factions in Fallout 4.
Personally, I'm really intrigued by the Minutemen, and the possible Redcoats. There could be a lot of fun characters, storytelling and loot tied to two factions like that. While I'm happy the Brotherhood is involved, I'm really glad that it seems we won't have to join them to use Power Armor!
Thanks, Paul! I've heard a lot of people talk about the Enclave being present, and while I certainly wouldn't mind it, I'm having a hard time seeing it work out. I mean, we know their advanced power armor will be in the game, but it's looking like power armor isn't tied as much to factions like in the past.
They've had their teeth kicked in in two games already, so I'm just thinking "How much more can they take?" If they were implemented in a subtler way, like in New Vegas, I can see it happening. But less so as a major faction. I don't want to see them go away forever, though.