Since Fallout 4 is going to be on the east coast, I can't really tell you what I want to see. I can however tell you what I don't want to see.
The Enclave: They've had their bases nuked 3 times already, they've suffered massive defeats, it's time for them to die. They should not be a main faction anymore, instead they should be presented as they are in FNV. Remnants of the faction that can give use insight into them and get rid of the whole "Enclave is evil" thing.
The Brotherhood of steel: They're being defeated on the west coast and Lyon's BoS has changed so much from the base group that it's not the BoS. Re-invent the faction as something that's new, grown from their BoS roots.
Supermutants: They should not be in as a faction at all. The fact that FEV was on the east coast at all kicked dirt in the face of the Lore.
Androids: This is just stupid and doesn't make any sense within the FO universe.
Basically, I want to see Bethesda get their own ideas and develop them, rather then relying on previous games to introduce a familiar face so people can identify it as Fallout. Groups like the BoS or the Enclave don't make or break a Fallout game. I want to see new things, new ways of doing things, new ideas, new conflicts. That's what Fallout is about.