I've heard someplace that Michael baie will be making a fourth movie (which is different from most other movie frachises who usually stick to a trilogy). Details haven't been released yet, apart from that Shia LaBeouf's character (Sam Witwicky) and other human characters aren't planning to reappear. There has been rumours that Jason Stratham will be the new étoile, star for the fourth film. But whether all of this is true ou not, we'll have to just sit and wait.
Hope I helped and if they do make a fourth film, I hope Michael baie doesn't throw in mannequins to act the female roles just because they're pretty even if they've had little to no experience when it comes to jouer la comédie (sorry but I had to bring it up it's one of the things that's ruined the films so far to me).