An interesting survey in Japan found that people were renting cars for: naps, as temporary work space, temporary storage, to charge devices, to have a private conversations, to eat lunch, and a few other things.
This is fascinating for a number of reasons. As the article points out a good amount of money that these companies make is from the miles that get driven. If a car is rented and then parked, they don't get as much money and so may start trying to tack a fee onto these stationary renters. Which they shouldn't. They should continue to provide the same value for the same product regardless of how the customer is using it and the fact that some people have found useful-for-them ways shouldn't be financially penalized.
But this is a very interesting thing to consider. If we abstract away from thinking about this as rental cars and instead as temporary contained space, the applications can get very interesting. Imagine being able to go to an empty lot, requesting a giant cube, throwing a party over the course of a few hours or hosting an event over the course of a few days, with septic tanks and gravity-fed water add-on options of course. General purpose, movable, temporary space-units could make for an interesting (good and bad I'm sure), future.