Michael Bay's "promise"

Whether you choose to believe it or not, personally I don't but Michael Bay has said that "it will be his last and the set the franchise up for the next guy". There really hasn't been much news about the next instalment in this dead on its legs franchise, nothing about anybody returning, no new castings nothing concrete at all.  

"There’s plenty more Transformer action to come with a major new video game release, “Transformers: Fall of Cybertron,” due in August and another Bay movie in the works. (The director, by the way, says that the fourth film will include some redesign of the robots and an entirely new cast. He also said it will be his last and set the franchise up “for the next guy.”)"

Well that doesn't seem to promising to me, it sounds like he is saying that he is making a new style of Transformers that the new director will be taking over from if/when he actually steps down. Why not just step back now an let somebody else take over the next "trilogy" now an he can be a guiding hand an help the along the way?