I understand why focus on mouse movement isn't feasible in macOS (moving mouse from a window to a menu bar could bring many windows unintentionally to the foreground), though there are utilities to do it with some delay.
A cleaner way to achieve this would be to change focus upon any keystroke based on the mouse's location. I think this should work so long as it doesn't change focus while menus are selected, though that might not even be an issue.
Is this something that can be achieved with BetterTouchTool? If not, is it feasible to add this feature?