It's fairly obvious to me that an open system, that incorporates Twitter-like functionality as a subset of a greater whole, could take over this space in less than 12 months, leaving Twitter/Facebook as AOL-like also rans.
Big statement. How do you get critical mass when practically every journalist, celebrity, and person you went to school with uses Twitter or Facebook and not your new open system?
While I definitely think an open solution could eventually "take over the space" and leave Twitter and Facebook as "AOL-like also rans," it's far from obvious to me how one would do it in a year.