Barricade will be back, won't he? Maybe TPTB won't want two 'bots that are both police cars, especially if one's an Autobot and one a Decepticon.
With how Michael Bay directs, it would be confusing...
There is a thread on another board what the film be like if Chris Nolan was directing transformers.
I'm trying to stay away from spoilers on the movie now.