I love how the brush now stays in the same position when rotating the canvas, so I wanted to suggest the same function for drawing selection boxes on a rotated canvas. If users are split on which they prefer, there could be a setting in the menu to toggle between this and the current behavior (drawing new selections in same orientation as the canvas) as the default. Keep being awesome!
Similar, or even more advanced/generic feature: bug 339077. I would suggest implementing that one instead.