I also haven't seen any here yet. I ride Citibike daily (Brooklyn and Manhattan) and would be wary of using the scooters because the roads are so badly maintained. It's already pretty bad even on a bike.
They haven't launched here. We barely even have dockless bikeshares (and even then they're not allowed in the exclusive Citibike coverage area). We're a rough regulatory environment.
It sucks to be in the largest city and yet could not try the scooters or electric bikes. I think it makes more sense for NYC to have them and would be a great way to avoid subway for like 2 miles.
NYC is also the most densely packed city in the US. There are places in the city where the sidewalks get so dense during commute/tourist hours that people cannot fit, pushing pedestrians out into the streets and bike lanes. 8th Ave north of Penn Station at 5:30pm is a prime example of this.
There's simply no room to have lots of discarded dockless bikes/scooters in such an environment where there isn't even enough room to walk, and they would be treated poorly. Docks/exclusion zones for the most congested foot traffic areas are necessary.