"you could get to the point where people purchase a car specifically for the intent of hiring it out for profit, in the same way that people do with yachts, holiday apartments and other high-value durables."
But, if it's profitable for me to buy a car for the purpose of renting it out, why shouldn't the startup cut me out and directly purchase cars to profitably rent out? And get economies of scale while they're at it? Maybe it's a way to bootstrap, but it seems like an unstable strategy, and that those purchasing cars to rent out are likely to find themselves on the receiving end of, ah, an uneconomical transaction.
Because the capital costs of purchasing and owning cars is huge. No startup is going to be able to compete with that. They literally need to use other peoples money. You could ask why AirBnB doesn't purchase apartments in New York and San Francisco.
A distributed model where other people contribute their money, and the business makes money as an agency is well established in other fields. I know of many holiday properties where each individual apartment is privately owned, but the building is managed by a single entity. The owners wear the depreciation costs and interest charges (if using borrowed money) but get to keep the majority of the revenue from rentals, and any capital appreciation from the property, or wear any losses from a drop in value.
In the same way, a startup can allow others to contribute the capital value, wear any depreciation, financing and insurance, and just take an agency fee. This is really not much different to other rental car companies who presumably lease all of the rental vehicles either off some central owner of the vehicles, or directly from the manufacturer. Or, perhaps they just have a large, revolving credit line which they use to purchase the vehicles. They certainly aren't going to own them, so it really comes down to a definition of title.
I think the blurring here is that most people see car ownership as a strictly private-use phenomonen, whereas in property or boats, mixed private/investment or pure investment is much more common.
I said "bootstrap", you described the "bootstrap", but as you may have guessed from the fact I distinguished the bootstrap case, what I'm really asking about is the eventual steady-state.
The cases you come up with are, to my understanding, management being hired out by a collective, not the management creating the collective in the first place. You also talk about a lot of entities who can obtain advantages of scale by bundling a lot of cars together. I submit that despite the fact you think you are arguing against me, you're actually arguing for my point. This startup in the long haul is going to look more like the central owner of the vehicles from an economic point of view than a neutral aggregator. It's the one in the position to make the most of all those issues and I just do not see how it can possibly be more economically efficient for little bits of rental here and there in the long term. They'll be used to bootstrap, then bumped out of the way when it's finally economical. Though hopefully they'll make some sort of profit in the meantime.
But, if it's profitable for me to buy a car for the purpose of renting it out, why shouldn't the startup cut me out and directly purchase cars to profitably rent out? And get economies of scale while they're at it? Maybe it's a way to bootstrap, but it seems like an unstable strategy, and that those purchasing cars to rent out are likely to find themselves on the receiving end of, ah, an uneconomical transaction.