Speaking of regions, some usability related improvements:
1. Perhaps tangentially related, but the ability to create/edit render regions numerically would be nice also:
e.g., 0,0-100,100 (Start at 0,0 for 100 pixel width, 100 pixel height)
2. Also, maybe allow them to be saved/restored to/from a config or XML file, so that you can save, hand edit, and later load a set of region definitions for areas of interest in the scene you are trying to tweak at any point in time. I think this would be a big time saver.
3. Finally, the ability to toggle on/off the visibility of the red region indicator rectangles and X would be a very big thing. For small regions, the region marking rectangle gets in the way of visibility sometimes.