Plot Details (SPOILERS)
It is also official that Episode VII will be taking place a little more than 40 years after the original trilogy and will be centered around the next generation of Skywalker and Solo. If stick to the expanded universe, It will be following Jaina Solo and Ben Skywalker.
One rumor that some websites have been circulating is that the villain will be a former disciple of Palpatine who will be trying to rediscover the might of the Sith Empire from the Old Republic. Hopefully this will turn out as exciting as it sounds!
All of my predictions take into consideration the fact that Star Wars is about to continue their Legacy comic book series, and they probably wouldnt do that if they are about to do a movie that unwrites everything they are about to do.
The movie will likely follow Jaina Solo, Ben Skywalker, Tahiri Veila, and Allana Solo. Jaina will have recently married Jag Fel. According to the Legacy series, Jag will eventually become the new Emperor and start an era of peace.
I believe that in this new trilogy we will see the rise of the Empire again, but this time done for good reasons. Jag will most likely found the Imperial knights with the help of Jaina Solo-Fel and his latest friend Tahiri Veila.
I believe we will also see the big screen debut of Darth Krayt (Asharad Hett). The books have been hinting at his exsistence as early as the clone wars, and in the latest book Vestara Khai leaves in search of other Sith to aid her. Krayt is a very interesting character and it would be interesting to see his red and black army of Sith rise.