This is just the type of opportunity that makes this potentially worthwhile, but not necessarily for every company or person: lots of problems that potentially can be solved, making it not easy for every company to succeed in the realm, but possible that some companies might.
In today's brainwashed anti-logic, no one is accountable, everyone is entitled, no one can be judged society, I don't see this working. But, let's assume that pendulum swings back the other way, enough that one can start doing some combo of the following:
- scoring the users (goes against the current trends of accountability and being judged)
- put cameras in the cars to make certain people are held accountable for their actions (goes against same current trends; even has laws against recording in California (!))
- Take a HUGE deposit before getting into the cars, so that any damage is paid for (this is still doable today, but rare: most people who might want to use these cars don't have a huge amount of money saved up, but perhaps this is just a decision they have to make, and a deposit level that works for each available car owner who rents will be found in the market by all involved)
- use AI to calculate the probability of problems for each pickup; the car sizes up the people approaching the rental, and zips off if they don't look up to snuff
- X-ray vision: if they are carrying a knife, bottle, pipe, cigar or other smoking implement, don't pick them up. Ditto on face grills, excess tats, crooked teeth, crooked unkempt clothing, etc. Perhaps the HEPA filter can take a "wiff", or a spectograph can take a quick look at their odors.
- Visual face recognition: find their Facebook, look at their postings, and friends' postings, and figure out how often they get smashed, and what time of day they get smashed at.
- I repeat my point #1: if we can score the users, making them furnish their driver's license (or identification card) every time, and verifying their ID with face recognition and perhaps also fingerprints, then we know their record.
- I could pre-approve each user by personal interview. What the heck? someone asks: yes. I can go door to door in my own neighborhood, sit down with each person, and figure out whether or not I think they are responsible enough to rent from me, and under what conditions (who they bring with them, what cargo and animals they bring, etc.) This could easily bring more than enough income, without having to go anonymous crazy nut case field of play. We don't have to think "Uber" every time we talk about the sharing economy.
- On the return trip, there might be people around who I haven't personally interviewed. Do I make use of shared judgement resources, or not? That is a value judgement I can make on my own: do I trust pooled value judgements? Which pools? Maybe my car brings them there, then waits for them, before bringing them back. Maybe after being alive for 30 years, I have personally interviewed enough people that the pool of users is large enough that there aren't that many empty legs.
You want to rent? The people renting to you will look you up, and require a lot of things. You want to buy? You pay more, and you can do what you want with it, within reason.
This is something the market can work out, as long as government and the anti-logic manifesto don't get in the way.
Until then, I agree with everyone else that says I don't want messy people in my car. This is relative to the cost and value of my car: if my car is worth Model S or X money: no way, ever. If it's worth Model 3 money: depends.
I could see this being a maturation process: a poor teenager decides they want to own their own car, and gets a used one, renting it out to friends. They quickly figure out that they can't trust all their friends, and they learn a little discipline, and this discipline gets spread around to some of the people they know, too. The next car they own costs a bit more, and they take better care of it, and have better friends. People grow up.
Will this all balance out, worth it to owners to rent out, ever, to a critical mass? We don't know. Buses are no good because they take forever, stink, disallow personal individualism, and can't safely carry cargo. Trains ditto. But, are rented cars the same? Obviously, rented cars carry some attributes from mass transit and some attributes from individual transit. No longer is sharing a vehicle often the domain of mass transit which shuttles welfare recipients around in a sort of maze of uselessness. Just what social structure will transport become, and will it be economical for this particular use? I think that's a decent question, and we don't have the exact answer right here right now.