On the 2nd point, most already explicitly exclude sublets and unlicensed rentals. Not directed at AirBnB, but due to shenanigans that have being going on for much longer. The short-term stays thing is relatively new (and largely popularized by AirBnB), but unlicensed rental for longer periods has long been common, especially in college towns, and insurance usually wants no part of it, especially in college towns.

(From what I understand, Couchsurfing is closer to a gray area, because of no money exchanged. Having a guest visit is considered a normal use of a home, and it's not clear if an insurance company could successfully argue that Couchsurfing guests aren't "real" guests.)