Tuning would be a concern indeed. I'm just doing somework for now.
As for rotor coating. It wears off over time anyway and besides, i've seen rotors with alky and nitrous sprayed on them and they were fine. If nitrous or alky doesn't strip em, time will. Either way, with the coating gone loses are minimal at best. Actully, I used to know a GPer in Colorado years ago (even went and met him once one summer). He used to dyno his GTP all the time. He took out his rotors and stripped them himself for his nitrous setup. On the dyno he only lost 2 or 3 HP with stripped rotors. Obviously his 100 shot later made up for that, and then some.
As for just a Turbo, I don't think thats quite for me. I want something a little different and I want to keep the blower.
If I went strictly Turbo, I wouldn't dick with a blocked off M90 personally, i'd get an L26 and start off on the right path IMO...