Repeat Last (action) Command

Because we are overhauling the UI and layering system anyway, I think a repeat last action key bind would help a LOT for symmetry based maps or in mapping architecture. I'm thinking of a similar function that Blender has with Shift+R, could even keep that key bind -if it isn't already taken- for simplicity. If this was incorporated into the line tool as well, it would streamline repetitive tasks.