Feature request: mask feather edge lines in the UI

It'd be very useful to know exactly where a mask ends once you start playing with its feather value. And since there's already a dotted line that shows up when using the feather pen tool, perhaps that same one can appear when modifying the regular feather value?
This would be great to avoid "ghost elements" left by mistake when animating out of a mask, by failing to  reach the absolute end of the feather gradient (I keep adding a black solid underneath and ramping up the preview exposure just to check if all elements are out of the mask's feather range!)

Incidentally, here's a secondary request... How about an editable feather value for shape layers? Adding "Fast box blur" to achieve this seems like extra calculations that could be easily avoided...