1. In order to operate safely they will have large operational constraints (i.e., they'll move slower, require wider gaps in traffic, etc.) that will make them less attractive than conventional vehicles.
2. They will be prohibitively expensive.
3. The combination of #1 and #2 means they will appeal to such a narrow group of prospective buyers that nobody will want to mass-produce them for a general consumer market.
In NYC, the cab drivers will work to kibosh their use, so for that matter will mass transit demagogues. I think the tech that makes sense involves certain kinds of braking assists, such as those feel-good ads that have been on for a number of years already, where the kid in the crosswalk's life is saved by the robotic braking hooked to radar or whatever.