1. They don't want to push the Supra price too high, just look at what happened when they did that w/ the MkIV. There's no way they can produce a V8 at the cost of a V6 price.
2. Yes it would. If they do that put a V8 in a "Supra" then it would need to be pushing at least 400 HP to be competitive w/ the Vette. Which mean it already push itself out of the 350Z class. Which I don't think they want to do.
3. For Purist, they don't want a V6, they want a Turbo I6. So I don't really know what you're saying w/ this point.