Exactly. Emissions are what holds things up all the time.

A while back Motortrend, or Car & Driver, R&T did an expose on a "Boss 351 Mustang" with a V10 rumbling under the hood. Completely one-off, prototypical and everything. In their limited testing they had already burned through a T-56, 3 clutches, and a couple of rear ends. I forget its power numbers - but if they put THAT motor in....