There's a rumor that the Miata and RX-7 will be soft- and hardtop versions of the same platform, with the Miata getting some kind of inline-four and the RX-7 getting the Renesis.

I don't think the RX-7 is going to be an "all-out performance car," but rather a lighter-weight alternative to the 350Z and new Supra (if it comes out).