I wouldn't worry about at all about losing the P90 character, and I would have no issues whatsoever with putting one in an SG. The Supermassive is still very much a P90, just with a strong and snarly midrange and more bottom end than a traditional design, while the high end has a smoother roll off.
It's a great pickup, very versatile indeed. I'm sure there will be some more conventional clips done in the future, and I'm keen to hear any users' opinions on them (and the Stockholms too for that matter).