Unbeeminders sounds good to me.
Re OP, what could be easily automated is an option to periodically remind about re-setting the goal rate.
Default is each, say, month you get a pop-up : “your current rate is X and you failed n times since it is so. Would you want to increase/decrease it ? Options : x.5 / x2 / enter new value / keep the same rate”.
It can be a somewhat obscure feature, doesn’t have to activate for new users, to not confuse them (or it could silently default to remind every month, tunable). Also, this could ignore the akrasia horizon since it is planned from long ago.
Re the third point, maybe the pop-up would say “you failed X times at any of your goals since last rate update” instead of being goal-tied. And maybe the rate update could be goal-specific, or global : every so often, be reminded to tune ALL your goal rates at once. In this case, the pop up could automatically mention : “maybe you are being too hard on yourself ?” / “maybe you would benefit from a bigger challenge ?”, depending on what the number of derails is.