I hate to say it, but this movie is going to have Disney playing it safe with what they know are successful ingredients and are not going to take risks. Therefore, the main character is going to be someone named Skywalker. In the unlikely even that it isn't, then the main character will at least be Luke's apprentice.
Yes, throughout the various novels, comic books and video games Star Wars has succesfully gone into any era with characters who aren't related to anyone seen in the movies. But Disney wants brand recognition, and face facts, more people know who Han Solo is than Grand Admiral Thrawn.