interesting that you mentioned doing a snippet, because i'm knee deep in a filter right now that needs this. i'm currently using curves and re-mapping, but it's not very elegant and because of some of the other controls i use, it's hard to keep a re-map correct for just one control, since others affect it.
and as for what shld happen, i'd just like fully masked, blanked out. you could also do it as an overly wide BG and just not show all the way out to the boundarie. whatever works.
and hadnt even thought of the blur, but yes, +1 there, as well.
If wishes were horses... there'd be a whole lot of horse crap to clean up!
Craig