Add an "automatically progressing goal" feature
This feature would allow a user to create a goal that automatically and gradually increases from a lower initial rate to a higher target rate. Inputs would be the initial rate, the final rate, and a time scale. The result would be a non-linear road that hits the target rate at the specified time. Preferably the schedule for increase (e.g., constant, decreasing, increasing, etc.) would be set automagically.
For instance, let's say I'd like to work my way up to flossing once a day, but right now I'd be happy with once a week. I'm pretty sure I'll fail if I shoot for the moon out of the gate, but have some confidence that I can slowly build up to it.
While you can do this manually, of course, this feature might help if you're akratic about maintaining your goals. I'd probably stick to a slowly increasing goal without even realizing that I'm improving.