Screenwriter Ehren Kruger, who wrote both Transformers: Revenge of the Fallen and Transformers: Dark of the Moon, is said to have an idea for both sequels, which Paramount Pictures is keen on. The development process is still very early though, and they are still hashing out ideas. It is said that rising costs for big-budget movies like this, and Hasbro's need for an increased licensing window, are a few reasons why they might go back-to-back.
One certainty for these sequels is Shia LaBeouf will definitely not return as Sam Witwicky. Insiders close to the production indicate Jason Statham's name has come up numerous times as a possible replacement for Shia LaBeouf. A formal offer hasn't been made to Jason Statham yet.
Michael Bay has previously stated that he will not return to direct Transfomers 4, although it looks like he may come back after all. Sources claim the director may be able to squeeze in his bodybuilding movie Pain and Gain before Transfomers 4. Paramount is eyeing a late 2012 or early 2013 start for Transfomers 4, so Michael Bay may be able to make Pain and Gain between then and now.
Transformers: Dark of the Moon raked in a whopping $1.19 billion at the worldwide box office, so it's only a matter of time before Transfomers 4 gets started.
Transformers: Age of Extinction was released June 27th, 2014 and stars Nicola Peltz, Mark Wahlberg, John Goodman, T.J. Miller, Stanley Tucci, Kelsey Grammer, Sophia Myles, Jack Reynor. The film is directed by Michael Bay.