Inter-monitor context-aware window snapping

A useful feature for people who use multiple monitors could be moving windows between monitors. Consider this example:

Let's say you have two monitors: Monitor 1 is on the left, monitor 2 is on the right, and a window on the right half of monitor 2 (aka to the far right of your monitors). If I want the window to snap to the left half of the second monitor, currently, I can set cmd+left to snap the window to the left half of the current monitor.

The feature I'm requesting, is the ability to hit cmd+left again and half the window move from the left of monitor 2 (the right monitor) to the right of monitor 1 (the left monitor). That is, cmd+left does not mean "snap to the left of the current monitor" it means "move to the left".

This could be done in halves, or it could be done based on the current window width. For example, if you have three windows splitting your screen you could have cmd+left mean "move to the left the 1/3rd of a screen width".

The way Double Pane implements this (as I recall) is:

def on_cmd_left()
  if not window.currently_snapped(): snap_left()
  else: move_left()