I would say that Bay will do exactly the same type of intro, if you have seen his sci-fi movies it's the same type of intro where someone narrates. Probably Optimus would say something like:
"Citizens of Earth, for some time we have lived among you, hiding in plain sight, protecting against you against a threat we thought extinguished. But we were wrong, I am Optimus Prime and now our war must become yours."
I actually got that off the Transformers: Revenge of the Fallen video game trailer. Also in the trailer it does reveal who is behind the Decepticon's symbol...it's the FALLEN.