A number of airlines have begun to be more stringent on the sizing of personal bags which passengers are allowed to take on-board. I've booked a flight with Lufthansa in Dec and their size limit on personal bags is just under 32" max.
Surprisingly [after doing a lot of online research], there are not a lot of choices for durable travel bags that are near the higher end of this range, eg. 28-32" maximum. At ~25", the Co-Pilot easily falls under the limit, but I can't help thinking that if the Co-Pilot were sized a little larger...I think 13x11x6 would be perfect, it would not only win over more potential customers as a personal bag option, but it would also be in tune with the needs of today's traveler. Modern laptops are now either 16:10 and 16:9 form factors and at 12", the Co-Pilot is not able to accommodate the current generation of ultra-portables and ultrabooks.
I'm still fixin' to buy a co-pilot this coming week to pair with my Aeronaut for the trip, but I would love to see if TB will either upsize the co-pilot slightly or introduce a modestly larger version. I've looked at most of the other bags that TB is making (with the exception of the messenger bags) and the next larger travel/briefcase bag that is larger than the co-pilot measures about 35"-36" if I recall.
In the meantime, keep up the good work...Tom Bihn bags are addictingl! I'm pretty sure I'll be getting a Synapse in the very near future.