Join Mask/Wall Polygons

A way to Join two regions by the hip by performing polygon addition would be great when finalizing a map. Rather than spending a large amount of time drawing a large overbearing mask over say.. an segmented antechamber, you could mask sections then just use a join tool to connect them all into a single mask. This would work great for walls covering negative spaces. I'd imagine it functioning like mask reveal tool, allowing one to click additional masks to chain join them. Ctrl-Z, Ctrl-Y to undo-redo the last join action.

This tool could simply check for shared points between the regions to determine wither they can be conjoint. A more complete solution is to determine the region of intersection and perform a seamless join over the intersected area.