Are you going to implement some simple rules (if price higher than X, sell.. etc.) or at least possibility to create bots as plugins? Btw. dividing app to server/client part would be awesome.
I think it'd be cool to have a little interpreter and a set of predefined variables and functions to implement stop-loss and bot logic, which could be stored as scripts. That is easier said than done but I'm working on charting for now which should any statistical analysis readily available.