The next engine was known to already exist back in 2007 but the page on Mazda's site for it is long gone. It was known in development as the 16x engine, but most of the community called it the 16c (to come after the 13b). The only solid information on the engine was that (at the time of development) it had up to 300 hp, a lengthened stroke, reduced width rotor housing, direct injection, and aluminum side housings. The two rotor engine was set to be a 1600cc engine giving each rotor 800cc which would have been been larger then the RX-8 and RX-7 engines.
What does this all mean?
The new engine for this car (SKYACTIVE-R Engine) will most likely be the 16x or 16c with Skyactive-R. If I had to guess, this thing will make 300HP and a bit more torque then any other RX before it. Everything is speculation at this point, but if Mazda is smart they will turbo this thing form the factory to give it 350hp. I honestly think that Mazda is making great progress with the engine and I am excited to see what comes out of this concept.