I think you could probably get close to the same affect with a subscription model, the only difference I could see is it creates a bit of a chicken and the egg problem. People won't sign up if the return is bad and people won't delegate if it isn't profitable. It has the potential to be a lot more work to try to convince people to delegate or subscribe and to be constantly trying to balance that out so that both sides stay happy, whereas with the bidbot script, the vote value and the token values basically act like a peg within a + or - 10% spread.

I think there's certainly a way to get a working subscription model though, I'll think on it for a bit and let you know if something solid comes to me.