I have had it hinted to me on two separate occasions that there will be further performance upgrades. Not promised, but definitely hinted. The last mention was in relation to P13 as I was wondering if it would be faster than the 12C. The suggestion was that by that time the 12C might be faster, still.
I agree it would be an excellent model, but financially would probably work best with a rapid development and release cycle. If they can shorten the product life cycle to 4 years, they can get cash from buyers who will be eager to upgrade to the next platform. The iPhone has always been better technology than the BlackBerry, but in the beginning it actually had far fewer features. However, RIM had no answer to Apple's pace of development and frequent product releases, which were largely enabled by Apple's choice of a better development platform to start with. So, not only does your iPhone get significantly better while you own it, you are still enticed to upgrade to the next one and start the process all over again.
McLaren's strength is rapid development of innovative technology. I think they are planning to out-develop the competition into irrelevance by keeping the benchmark moving ahead so quickly that nobody can keep up (literally).