If it works that is. If it can get to your home and to your job, not 4 miles from your home and 5 miles from your job, but door to door service, any time of day or night, and no mileage limit. This must include the uncool places where real people live, suburbs, rural towns. Today we have huge number of people commuting from suburb to suburb, the old hub model is dead and no one wants to go to a crime ridden and grime filled downtown. Nobody puts a technology park in an urban core.
If some people today can use mass transit, then that is great. However it is not the norm and not something you can expect everyone today given the huge limitations it has.
Self driving cars could fix some of this, but I see a lot that it won't fix. For one, it's not 'mass transit' and it's not even 'car pool', it won't reduce the number of cars on the road and it won't encourage mass transit to move away from downtown and out to where people need it.