Doflamingo wants to be Pirate King
Joins the fray without his crew
My body can't handle this awesomeness
I think Doflamingo will be the reason why Law and Luffy will have to separate ways. I'm sure the Yonkou they were talking about is Shanks and it's too early for him to get involved.
Maybe he will just grab Ceasar, wrecks the team, and gets out of the scene. Since Ceasar is already the "boss" of this arc I doubt he will get involved much.