The Tom Bihn Western Flyer - a nifty and versatile less-than-max-sized carryon - is now available with traditional backpack straps. It is still also available in its original mono sling strap configuration. More to come.
I’ll be receiving a WF with backpack straps in a week or two for a hands-on trial. Darcy at TB says the the backpack straps are all new and are very comfortable. My original review of the Western Flyer is here.