Do You Think SF or NYC Public Transportation System Could Use This?

I've seen something like this demo'd in NYC, unfortunately I can't remember if it was a NY Tech Meetup or other event, in the last six-eight months.

The NYC Metrocards come in two flavors: unlimited (day, week, and month) and pay as you go dollar denominated. The dollar denominated ones are topped up in such a way that you get n bonus dollars (essentially additional rides) for every X dollars. It had been the case that if you only use your metrocard on the subway and most buses then you don't end up with odd dollar amounts on the card. But certain buses (typically express buses) charge more than "one ride" (whatever that currently is, $2.50 I think), however with the last fare increase they did not adjust the bonus so now you do end up with odd dollar amounts.

There's also an automatic refill "pay as you go" card, the EasyPayXPress Metrocard which can be filled from a credit/debit card.

Fares are discussed here: http://www.mta.info/metrocard/mcgtreng.htm#payper

As to whether it would be useful? Sure? Maybe? In NYC most subway stations have metrocard vending machines where you can top up, but almost no bus stops do.

The MTA is in the very slow process of evaluating MetroCard replacements and options (there's been multiple NFC-ish experiments with fobs and credit cards), now would be a good time to contact the MTA if you have something that can add value (and scale).