Guest-Stars are a big thing. They ultimately determine where BP will fit in MU. If most of their guest-stars are Avengers (team or individuals) or the FF, then he will be part of the broader "MU" family. If most of his guest-stars are X-men, he will be pulled into the X-family of books (which I personally think would be a mistake). If Spidey did the most guest-starring, then he...nah, even that wouldn't pull him into the Spidey-family, but if most of his team-ups where with Spidey, DD, Iron Fist and even Cap, he might be considered part of the "street heroes" of MU.
Villians can have the same effect.
Personally I want him in the Avenger/FF family of books.