The question is, why would they do that? Surely promotional content is published after the entire development process is complete? Why would they use an unfinished car in a poster that was posted for a DLC that, at the time, was only a couple of days away from release? (actually I'm not entirely sure when the pic with the Mazda popped up so if anyone could tell me when that'd be great) The description is still intact - "Add the best of Europe, Japan & the United States of America to your car collection with this new bundle. " It's probably due to licensing issues or other reasons, but I think everything is pointing towards the fact that the RX-7 was originally meant to be in the DLC. Not sure if it matters, but IVT already holds a Mazda licence for the Laguna Seca stuff. Perhaps another reason could be that they weren't able to finish making the car in time. And after all the delays, mishaps, glaring oversights, 'technical issues', in particular the recent Patch which pretty much failed to fix most of what was on the notes, I don't find that too hard to believe.
I still love the game though ^-^