Technically, the cabs are already great at what they do. They quickly and reasonably cheaply (considering) get you from point A to B. But the biggest problems I've had with cabs have had less to do with tech than human factors.
For example: Advertisements. Someone thought it would be a good idea to fill cabs with loudspeakers and screens that subject the passenger to one-way advertisements. I'm annoyed by this because A: It's unpleasant to be so aggressively marketed to and B: I didn't think of it first. If there was a way to equip cabs w/ a basic data terminal that used GPS to bring up relevant data regarding where I was (or services near my destination), that would be brilliant.
Also, the credit-card issue is slowly being addressed. It's gotten much better, but everyone still runs into some cabbie who makes a big show about pulling a manual card-swipe out of the trunk. Give me a debit-style terminal in the back seat like a freakin' grocery store.
Instead of political issues like electric cabs, let's see an improvement on the end-user experience. The rest will happen on their own as business owners start seeing a financial advantage.