Square actually approached the NYC tlc about replacing current systems. That experiment will be happening some time in the next year. Likewise there will be several other services enterIng the market this fall, some of which have some very interesting ideas for the market and are currently in quasi stealth mode
I have some personal knowledge about /involvement one of the projects underway. Theres some really interesting mathematical and algorithmic challenges that pop up from the get go in trying to create interesting product/service and build software that works™ (I'm talking problems where the perfect information versions with deterministic outcomes are NP-Hard, but then you add an online new info component and probability on top of that.).
Anyone who'd like to learn more about that stuff and is in NYC (and not affiliated with other companies in the same space), drop me a line and I'm more than happy to chat about the space in more detail :)