A lot of this article will be handicapped by the fact that I barely remember the first three Transformer films. So I can't confidently claim no awesome actors have ever voiced Transformers before (save for Tom Kenny! and a completely unrecognizable Hugo Weaving). I can't even be confident that we've never had a broad Asian stereotype Transformer. Seems like we probably should have, but none come to mind because "mind" and "Transformers" are generally not good bedfellows.
So let me just pretend that Transformers: Age of Extinction will be the first Transformers movie to feature awesome actors doing Transformer voice work and/or broad Asian stereotypes. Word has come down that both John Goodman (another Coen Bros. actor) and Ken Watanabe have joined the cast as two "all new Autobots."
So one of these Transformers will have a deep, authoritative baritone. And one will have a Japanese accent. I don't actually know that Watanabe's Transformer will be a broad caricature. But I have seen three Michael Bay Transformers movies and know basic math.