I would like to see the storyline of New Reno continueing off of Tactics.
What I mean is not Midwest BOS vs. West Coast BOS. I find that match up highly unlikely since the Calculator probably finished off the West Coast BOS who were highly weakened in FO2 and not likely to have made any kind of recovery. Remember they sent their expedition after FO1 and by the time we see them in FO2 they have only one in-game member and lots of empty bases. Combined with this obviously weakened state and the rise of NCR as well as the possible and likely ending of Tactics being the Calculator taking over the Midwest BOS and eradicating the remaining West Coast BOS I find a war between these two highly unlikely in Fallout New Vegas. Most likely the antagonists will be the two shown in the opening video (not spetznaz either). Robots and NCR going at it.
Why not?
Fallout Four: Enclave and Brotherhood Alliance
I also believe and hope that the Enclave will appear in Fallout 4 alongside the BOS. A new and unheard of enemy will force the Enclave/BOS into a sort of shaky alliance. This could possibly be the Commonwealth or some terrible thing they cooked up. I would bet when we finnally explore the Commonwealth it will be a blasted battleground with BOS and Enclave fighting desperately against some kind of terrifying new enemy that has already destroyed the Commonwealth who created it and threatens humanity as a species if it is not contained. Remember that the Enclave has been left leaderless and the Brotherhood East Coast is led by Lyons. This alliance could happen given the need for it.
Why not?
These are simply my ideas and hopes for future Fallout games and enemies.