Sharing economy type stuff makes complete sense when it's something you share often enough to want first dibs, but not often enough that renting it out from time to time is an inconvenience. But if you're renting it out full time then I'm not sure I understand how the incentives line up. Seems like if they notice you're doing well they could just swoop in and under-cut you next time the contract is up.
What's interesting is if car manufacturers start to develop vehicles specifically for this kind of market. I'd love to have personalization settings (nav, seat, climate, driving controls, etc.) which follow me as a driver across a fleet of identical or related vehicles. You might also have a "valet mode" (some cars do now), "renter mode", and "owner mode", with different performance limits (I can ruin a $1-2k set of tires in 10k miles of spirited driving, but if I ran the right profile on the car, I could make them last 30k miles). Might also make some maintenance/safety things non-overrideable for renters -- you can't start the vehicle if the brakes/tires/fluids/etc. are not good, for insurance and vehicle-damage reasons.
I tend to buy/keep cars ~forever, so it wouldn't work as well for me now, but if I could lease ~3-5 BMWs for ~20-30 people to share (at a remote company office or something which has a lot of people cycling through, and where some cars are needed), and then add them to a fleet pool otherwise, I'd be in. That's somewhere between Zipcar, Uber, and leased company cars.
Managing maintenance, cleaning, insurance, repairs, etc. for them for me would be great, too.