Joan Allen has become a staple of the Bourne franchise, more so than anyone else [except for Matt Damon, obviously]. She was most recently seen in The Bourne Legacy, having played an integral role in all four Bourne films, but will she appear in the Bourne Legacy sequel?
The new star of the series, Jeremy Renner, is incredibly busy and so far doesn't seem to have time for the Bourne Legacy sequel anywhere in the next two years. After the first film performed decently well at the box office, there was a lot of talk from Universal about the sequel and setting up the new franchise, and possibly bringing back Matt Damon to the next one.
However, this talk quietly tapered off after a while. What happened to it? Well, it could be somewhat of a combination of other films on Universal's slate, working on getting the script right, or disinterest from the actors/director/writers/studio executives. Since the Bourne Legacy did fairly well at the box office, I don't think it's monetary concerns.
Either way, if the film does or doesn't come back, it will be interesting to see if Allen will return to the series. She hasn't been seen in anything since 'The Bourne Legacy', although she does have a film called 'A Good Marriage' set to come out on sometime in soon.