There's no particular reason that wouldn't be successful, but it makes about as much sense as them branching out into the ketchup-making business.
Being a Marriott hotel means you have access to Marriott customers on Marriott.com and other sites through their systems. That's not much different than AirBnB.
They may as well take that money, and invest it into <Insert non-core competency of AirBnB>. Or, alternatively, partner with an existing hotel franchise.
Managing other people's properties, on the other hand, is a natural extension of their core business.
http://marketrealist.com/2014/10/why-marriotts-hotels-have-s...
What'll someone's happen is that the building and management don't change, yet the hotel brand will change.
and liability