The main catalyst for possibly restoring theoriginal "Prime" timeline, and/or uniting the timelines is Prime Spock being alive and well in the altered universe.Spock has the knowledge of the "Jellyfish" ship,red matter,the "possible" future,etc..We are being asked to believe that this is the same Trek universe thuse altered because of future Spock's/Nero's actions.If Nero were to be stopped in the future somehow before he got a chance to go into the past or if his reason for doing so were averted/quelled, then this would completely eradicate all actions that changed the past because he(Nero) would never have traveled into the past to destroy the Kelvin(thus restoring Kirk's original rise to Enterprise captain), destroy Vulcan, or wait for Spock to arrive.
Again, not saying this should or ever will happen as it's VERY unlikely(in the movies at lesat).The new timeline does figure into the new Trek mmorpg where they have been writing a new history for post Nemsis Federation(Klingnons,Romulans, etc.)and the events of the new movie are worked into Trek canon/history there without changing very much about Trek's future (24th century at least)as we still have a Picard who is now an ambassador but was once the captain of the Enterprise D and E etc.,etc.,etc..For arguments sake, Old Spock is likely trapped in the alternate timeline in which Vulcan was destroyed whereas "Prime" Vulcan is very much intact in the original timeline that Nero and Old Spock traveled from.Not only did Nero and Spock travel into the past, but they did so to the past of an alternate universe.I believe that is the story. Kutrzman and Orci are using.