The pack looks great. What did you use to make the stretch on the pocket? Is it just lycra? How well will the pack compress down, for instance, if I didn't have enough gear to fill it up high? Can you reach the bottles in the pocket without taking the pack off?
The only couple of construction techniques that I would think to change are on adding the haul loop and reinforcement patch on the back panel. I personally don't like to see raw edges whenever I can hide them, so I put the haul loop under the patch and roll the edges of the patch under a quarter of an inch and sew them down. I'm not sure how much dyneema x frays (it seems like it wouldn't) but it has made a difference on lighter fabrics for me and it is something really easy to do.
The pack looks really promising. Good luck with your venture into producing gear.