I use a monitor that I can rotate 90 degrees, which makes portrait photos and standing models a lot more fun to draw. The models usually become as large as possible, while they would only fill a third of the screen in landscape mode.
My idea is this:
Categorize images by their orientation: portrait, landscape, and "neutral" (for when it's close to a square photo that works in either orientation)
Either let us filter by orientation as with view/pose/etc., or make a portrait and landscape mode. The result would be the same.
It would be a great addition for everyone who has a flexible screen.