Just this week in Vantaa, Finland three 12-year-old girls piled onto one of those electric scooters you subscribe to with an app and proceeded to get run over by a car at a crossing, killing one of them
The app is supposed to have an age restriction but it's easy to bypass and you're not supposed to have more than one person riding on one, which people routinely ignore
I hate seeing kids and teens speeding around dangerously on those fucking things and then just leaving them laying around on high-traffic bike routes because they don't give a shit since they treat the scooters as completely disposable
Fucking awful bazinga-brained Silicon Valley-ass idea and business model. Actually, there are also bikes you can use with an app but curiously you don't see kids doing reckless shit with those, almost as if electric scooters were uniquely terrible 
I assumed that. You can see your imaginary scenario play out in plenty of areas and it doesn't go to well most of the time. People are going from point a to point b and that means they're trying to go with some speed. If you make the traffic environment uncertain/unsafe then you get collisions and tensions. This isn't black&white, there's times where mixed-use with poor signage can be a good idea, but it's mainly for recreational areas that make it clear to all that they need to be aware of their surrounding. As general traffic planning it's not a good go-to.