Longer term I'd actually like to make safety buffer be meaningful for weight loss and inbox zero goals by generalizing the Pessimistic Presumptive Reports that currently are only used for Do Less goals. This is an ongoing debate with @bee but I think I'm going to win eventually. 
Here's my latest thinking on it: First, assume we've switched to the yellow brick halfplane new world order where there is no centerline or lanes of the road. Instead there's only the critical edge, plus colored zones indicating how close you are to hitting the critical edge. [1] Next, we ask you as part of goal creation what's the most amount of weight you can gain in a day or the most your inbox count can jump up in a day. That's the Pessimistic Presumptive Report -- explicitly chosen by the user.
(Technical aside: The colored zones should have width of yaw*(rate - ppr) where yaw is +1 if the good side of the road is up and -1 if the good side is down; and rate is the daily rate of the yellow brick road.)
The result is that it becomes universally true for all types of goals that you transition from green to blue to orange to red -- one per day -- if you don't report new data. For example, imagine a weight "loss" goal that's in fact just to maintain a constant weight. And say you put in 1 pound as the amount your weight can fluctuate day-to-day. Even if you get the stomach flu and lose like 8 pounds and are way below the yellow brick road, you still can't stick your head in the sand not weighing in while you gradually end up hopelessly far above the road. You just have 8 days before the PPRs catch up to you. This also makes it much nicer for maintaining a safety buffer for vacations.
In short, safety buffer needs to always be meaningful and reasonable.
[1] Totally on board with @grayson's dark green idea, btw, which may not need to wait for yellow brick halfplane -- keep clicking 
on her post especially if you don't want to wait that long!)
