Originally Posted by SuperT
I think "undoing" is the wrong word to use. He certainly isn't just going to up an erase the original timeline he himself created, but I could absolutely see the 70's timeline and then the original timeline breaking off into two alternate timelines a la Star Trek 2009. (I know I keep bringing that up, but it's the best example)
Honestly, that makes the most sense.
I think that is very likely the direction DofP will take. It's an elegant solution that preserves the events of the original films (by that I mean X1-X3, maybe Origins), deals with concerns over matching up the events in First Class and its sequels with the time period of the original films, and wipes the slate clean for going forward.