So this article
came out today and basically said that Kathleen Kennedy got shot down by the Mouse for asking for an extension for Ep 7's release. Things cited in the article were Kathleen and Abrams bickering over casting decisions and Arndt spending too much time (and money) working on script rewrites. This explains Abrams and Kasdan taking over scriptwriting duties. The article also says that Abrams is more in line w/ Disney wanting to hit the 2015 release date. This leads me to believe that Abrams is waiting for his big payday. Very likely he only got a small chunk up front and has a big deal in place where he'll get film & merchandising points. He won't get hugely paid until the film is released so of course he would want it to come out ASAP. Course this is risky, because if the film is crap, those paychecks won't be as big as he's hoping for.
The studio demanding time constraints on the film is why George kept his company independent for so long. He didn't want to have to answer to anyone. He could set his own time schedules and any delays were on him only. Can a "Star Wars" movie be made in only a year and a half? Sure. We're 10 years now after "Revenge of the Sith" thanks to the CGI technology advances that George made w/ his films, movies can be made a lot faster now; just think of how quickly the Harry Potter films were cranked out w/o any loss of quality. Abrams wanting to do the film on standard film rather than film it in HD might cause some delays, but that'll be on his head if it happens.
I think at this point fans should start getting worried, there's been nothing but shufflings behind the scenes and nothing announced about the film actually moving forward, which is lovely considering it's supposed to go into full production in like January. I would think that they would need time to start choreographing fight scenes, fitting costumes, etc w/ the actors, that was always a big part of the pre-production periods that George built into his 3 year plans for the other films.
Who knows - maybe they'll just cast everyone from "Spartacus" so they won't have to train them to use lightsabers.