They are not necessarily dependent on partnerships with taxi services, why would they? Anyone with a license will probably be able to sign up on their platform and start benefiting from the tools TAXI token is going to provide. That alone creates a lot of advantages and then even taxi services might decide to sign up to not miss out on the opportunity.
robotic taxis programmed via blockchain? :-D #sci-fi
I wouldn't say it is that much of a science fiction scenario. It's gonna take some more years, but it will happen that self-driving taxis will be ordered via a decentralized system.
Tesla corp is well placed to provide the self-driving taxi service, but it might take some time and it won't probably happen in our lifetime
Elon Musk is a clever fellow, so I don't think that it's impossible to implement such an ambitious project. It would be one of the greatest innovation of the 21st century