This is what Tyrese Gibson had to say about his own return in Transfomers 4, and the possibility of Steven Spielberg directing.
"If Michael Bay decides to come back for Transfomers 4, I'll be there. We'll make it happen. (Right now), I think we are all exhausted with the process. If this movie does what we are all assuming it's going to do, then, I think its time to revisit this conversation. When it's time. There are no concepts, no direction, no nothing for Transfomers 4, because everyone has been so focused onTransformers: Dark of the Moon. But here is the safety net. Are you ready for this? Michael Bay decides to not come back for Transfomers 4. There is alwaysSteven Spielberg! I am not saying that Steven Spielberg is for a fact going to direct Transfomers 4. But it is a beautiful safety net to know that one of the biggest, most respected directors in the world happens to be an executive producer on Transformers. He is someone who knows this world. And he could easily step in and direct Transfomers 4 if he decided to. The thing is, there are a lot of directors who deal with producers who happen to not be Steven Spielberg. So if the director decides to bow out of their film, they are sent scrambling. "Who can we get to direct this?" What a hell of a safety net this is if Michael Baydecides not to come back. Steven Spielberg could easily step in and make it happen."
Credit to movieweb.com