This model works with cars (e.g. ZipCar) but with scooters I don't see how this is possible, unless the entire city is quite literally littered with scooters.
If I have to walk 5-10 min to the nearest car which I can unlock from my phone and then use to drive 5 miles somewhere then it's great, but if I have to walk 5-10 minutes to the nearest scooter pickup so I can scooter somewhere for 5-10 minutes then it sort of defeats the whole point.
If you have to walk 3 blocks for a scooter, then they really aren't "ubiquitous", I'm not a scooter user, but they seem to litter the sidewalks around here, so it's usually only a 1 or 2 minute walk.
As you said, if it's much longer than that, then there's no point -- I don't think I'd want to ride a scooter more than a mile or so anyway, so if it takes me 10 minutes to find one, I may as well just walk the whole way.
Even in LA which has a huge number of scooters, there's been times where I've scooted someplace then when I turn around to leave someone unlocked it.
If it's getting later in the day most of the scooters you find are going to be scattered in all sorts of very strange areas, many times in gated apartments, and/or with not enough charge to get you home. Or maybe you have to settle for that scooter with the screen dangling out of it by the wires and the handlebars at 45* relative to the wheel that everyone else was just not desperate enough to use.
If I have to walk 5-10 min to the nearest car which I can unlock from my phone and then use to drive 5 miles somewhere then it's great, but if I have to walk 5-10 minutes to the nearest scooter pickup so I can scooter somewhere for 5-10 minutes then it sort of defeats the whole point.