This would be cool as a menu bar application that shows up when it detects an external display, sort of like a rear-view mirror for my Mac. I wonder if it would be possible to move things around inside it with the accessibility APIs that window managers use.
As in creating a virtual display and mirroring that into a window (instead of mirroring an existing display)? There was an HN post[0] about a piece of software called DeskPad about 8 months ago that does exactly that.
BetterDisplay can also do both, as well as a truckload of other things (some free, some paid).
