I think it was mentioned before in some of the engine discussions. I can't remember how heavy it is. To me it would have looked like an interesting choice. At least if they can get the originally claimed 250HP out of it. As it's currently in the RX-8, it doesn't seem to make much more power than the Toyota engine we got.
Currently it makes about the same power and gets 14-16mpg, though some people are getting as high as 20mpg. Power is being limited by some epa required ecu changes. Supposedly the computer goes rich at the high rpm levels to cool the charge temp and allow the cats to live longer.
Weight is less, and it has a lower center of gravity. Cooling requirements are higher which may offset weight savings. FI would have a marked improvement in both torque and overal hp, with the current 13brew engine hitting 600+rwhp using some fairly extensive cooling/fueling mods. The Renesis may not be able to go quite that high, but should easily be able to throw around 350+rwhp FI. Problem is still fuel usage and where do you put the intercooler?