This reminds me of the startup idea generator that spat out "airbnb for workouts". My reaction to the basic idea is the same I had for a startup I saw on Shark Tank (I think), which was airbnb for pools. And that reaction is: ewwww, no thanks.
I just can't imagine ever using such a thing. Of course, I'm not a gym user in general so take my opinion with a grain of salt.
Interesting idea, sounds like a nightmare for insurance underwriters though, if according to the T&C hosts are to obtain insurance on their own? Merely curious: does anyone know any providers who would underwrite a policy that covers you in case a total stranger hurts themselves on your leg press?