I’m really down with Nourmalaeb’s Velcrometre concept. As drawn it looks like the straps would fail pretty easily, smashing your precious cargo, but if you ran the straps 180 degrees (or 360) around the bag with velcro to velcro contact over one entire side of the bag for each strap I think you’d have a very feasible chance of this actually working. If any of you haven’t experienced industrial strength velcro before, that stuff holds so well that sometimes it’s hard to get it apart! For the messenger style you could run the strap around the sides and bottom, I think that would work quite well.
I really like the fun involved in it, being able to set it up any way you like, and the idea that at any given day your bag might not look quite the same as it did the day before. Also I think the constant little velcro noises it produces would be fun (maybe not in class tho as Ineo pointed out). This is the kind of thing I would definitely buy, even if i didn’t use it on a day to day basis. Well done!