FR: Resize on one axis if mouse near edge and far from corner
So if the mouse was near the left border of the window and far from the top & bottom, then the resizing would only move the left edge. How hard would this be to do? Something like this diagram:

If I understand your reasoning, you actually mean that if the cursor is not touching the red area, the window should resize ~vertically~ horizontally and keeping the opposite corners stationary?
- "near [...] border"
- "far from the top & bottom [border]"

Did you mean "resize horizontally"? I mean that the edge you're near is what should move. So in your diagram, if the mouse is in the left white area, then the left edge of the window can go left and right, but the other three edges of the window are fixed, so it's only horizontal scaling. I was thinking that the left triangle in my diagram would correspond to the left edge, but your rectangle might make more sense.
Excuse me, I meant "horizontally".