Grimlock is the exact character that should replace ironhide. He is a perfect match and for all intensive purposes he is unquestionably the single strongest transformer.
I personally think that the Dinobots in general could easily be incorporated into the story. After all they have been here a long time right? The Dinobots could simply be a group that has no faction that have been on Earth for a long time. We need a character that is more powerful than Prime. Frankly Prime has evolved into something that lacks any real challenger. The conflicts between Grimlock and prime just as it was in G1 early on would be pretty impressive.