I have a beautiful co-pilot and my partner has an aeronaut and a synapse. i still have a roll-aboard and have been ruminating and generally over-thinking which bag i want to replace the roll-aboard with. so i've been playing with the aeronaut and was thinking how great it would be if the co-pilot fit into one of the end pockets (and then could be taken out once on board the plane/boat/train/camel - i.e. containing all of the goodies that you want easy access to while en voyage). but, alas, it does not fit (unless you cram it in and fold it over slightly - something you couldn't do if it was full of goodies and goods). so, just a thought, but it would be really cool if there was a way to build future bags that could accommodate other bags. well, specifically, i'd love to be able to fit a co-pilot into the end pocket of the aeronaut.