I am currently awaiting the delivery of my new Zephyr. Any day now.
In the meantime, I was reading the "Wheels" thread, and realized that the reason a lot of my colleagues switched to a wheeled bag was because of back problems. Most on the advice of their chiropractors, they've given up on shoulder strap bags. Of course, they've now also given up on wheeled bags, so they have nowhere to go.
What we really need, of course, is a backpack that doesn't look like one when we get to the customer. It should feel great at the airport, but before we get to our destination, we dash into a phone booth, and come out with something that looks like an Empire Builder. All storage and symmetry when travelling, all classy and professional when you get there.
OK, maybe less magic, but maybe a briefcase that has some removeable backpack straps, or fits into a backpack harness.
I'm not sure how you design stuff, but maybe if you left a Brain Bag and a Zephyr together in a dark room overnight, with some romantic music, you'd get the answer.