I seem to recall their original model being around paid developer access to the platform. That is fairly intriguing as the ability to create value-added tools/techs and partner with any other discount brokerage is very difficult. Seems like a large enough user base would enable an app-marketplace where many of the quant/social-stream/chatter-arbitrage tools that currently [try to] sell direct to investors could have a chance at more distribution. Couple this with something like Quantopian ... profit!