Okay, Tom, I want to re-open this discussion (it got lost when the forums went kaplooey.)
Carry-on travel bags, for those of us who wish to avoid getting our luggage lost or schlep around with a suitcase, are expensive, ungainly, poorly designed, and increasingly oversized. You are totally the guy for this job.
That bag I want:
* Conforms to actual carry-on standard size.
* Is convertible between backpack straps and a shoulder strap.
* Has a waist strap for stability/to prevent back strain, removable chest straps if needed.
* Has a much better compression setup inside. Two narrow straps are only slighly suckier than X-shaped straps. Please think of something brilliant.
* NO WHEELS!
* I won't say no frame in all caps, but if there is any kind of frame, it better not weigh anything.
* Some sort of lock or clip for all zippers to help avoid pickpockets, without actually requiring keys and locks to get to the stuff.
* Handy zipper pocket on outside somewhere that's reachable without taking off the whole bag.
* Lock-able for real, with locks, when necessary.
* Thingy for water bottle.
(I believe you already are aware of One Bag ?)