Don't want to sound like a advertising or something, but what you are describing is very similar to the services (or you can call it long-term activity), that our platform CHAOEX currently offer. We are paying daily interest to all the users, whose total assets exceeding 300 usd. equal in any token/coin or combination of several. Though we do not promise huge returns, but more like a appreciation for users' trust, we still believe that the idea of paying interest is great and want to develop it into separate product.