I have been agonizing over whether to buy the Western Flyer or not myself. Thanks for starting the discussion! It is interesting to read that there is a possibility of a bag yet to come between the Flyer and the Aeronaut. I do not actually need a bag until next April. Maybe I will force myself to sit on my hands, away from the credit card when viewing the Bihn web site :-)
I think it was at the One Bag One World web site that I saw a post about looking for the lowest common denominator for bag sizes. Someone figured that 19x13x8 would suit about all airlines.
Looking at some pictures of the Western Flyer and how even a 7" bag swells outward, I think I would love a 19x13x7 bag that weighs 2 lbs or a smidgin over.
I guess I would like convertible straps, too, though to leave them off and only use a quality shoulder strap would help save some weight (plus leaving all the "I might need that" items at home!).