- investing in such a fleet would be like investing in any other kind of business: it's easier if you have the money, but if not you can go to any bank and get a loan.

- prices for a trip with a self-driving taxi will drop immensely, this is probably going to be a big liability if you would start the aforementioned business

- other effects that I can't think of right now

It is true that in a lot of places rich people have an edge on the less-wealthy (it's easier getting/staying rich if you are rich), but that's more of a generic problem than something that would be amplified by change to self-driving cars.