While there are some valid points there, I think most of those benefits can be realized to some extent without anyone needing to actually "own" any of these cars.
> using cars for storage
While it's true that you won't be able to just stash all your stuff in a car you don't own forever, I think it's entirely feasible to have a system that lets you rent a car for a day to use in this manner. Obviously not quite as good as owning a car, but you can get a lot of the same benefits in limited circumstances.
> being readily available
I think under most circumstances shared cars will actually be more "readily available" than a car you own. Once autonomous ridesharing services reach a certain level of market penetration, it's practically guaranteed there'll be a car less than a minute away whenever and wherever you call for one. Plus there's no need to worry about where you parked, whether your car is out for repairs, or whether you can drive home without leaving your friend who hitched a ride with you on the way there stranded without a vehicle.
> lower cost of owning
Wouldn't a shared vehicle actually cost less, since the cost is split among all the different people using it?
> reduced insurances
Again, probably be cheaper with shared vehicles, since the driverless car company can self-insure.
> customizations
Yeah, this you'd probably lose with shared vehicles. No more bumper stickers or vinyl wraps. Though there may still be a way to pick a car of a specific brand or paint job if you so desire.