Last year I spent several months shopping for the 'perfect' lightweight pack. I settled on a ULA Conduit for just over $100. My comments on your prototype will be referenced to my experiences with this popular ULA pack... the features and benefits I like, plus its shortcomings.
Size/weight - don't know how you are measuring, but my ULA at 50L weighs 16.9 oz without hip pockets. So far, the material of the ULA seems pretty durable.
1. Hydration sleeve - I don't consider these set-ups as lightweight. Not necessary.
2. Shoulder strap pockets - make them optional and removable. I sometimes use a couple MLD pockets with my ULA at .5 oz each and a perfect size. Still need to figure a better method to keep them from sliding. They use those plastic strap quick clips. Probably sewing the web strap to the wider fabric, about 1" below where the web is attached would work. I like to keep my camera in one, because I don't feel comfortable keeping this expensive item in a hip pocket when I remove the pack and lay it on the ground. I like the MLD Velcro closure, plus the plastic snap.
3. I like 3 mesh pockets. Especially to stuff a wet poncho in, or keep tent stakes and wind gear in. If it is tight, you aren't going to stuff a lot of stuff in them. I like to keep a water bottle in each side pocket. Your side pockets look too tall. The ULA has much smaller pockets and are angled for easy access to water bottles. Problem is a 1 liter platy will fall out of the ULA side pocket, requiring a heavier Gatoraide bottle. I am thinking about asking Brian if he can redo mine with no angle, or a higher angle. I have never seen an angled side pocket that is truly easy to access while moving anyway. For me, I usually just stop and take a water break, or just sling the pack on one shoulder, take out the bottle and drink while walking. You need to be a contortionist to grab something from a side pocket, IMO.
4. Top - roll top extension collar. More capacity if needed. I have a MLD top lid which I sometimes use with my ULA. Doesn't fit perfectly and weighs 2.5 oz, but can be useful once in a while. The top lid stays at home most of the time. An extension roll top is a versatile option.
5. Short torso... ultralight pack doesn't need to shift a lot of weight to the hips. I like the belt high. On a heavy pack, it needs to be lower.
6. Load lifter straps... extra weight and marketing hype.
Notes on #5 & #6, I am 5' 11" and it is easy for me to find a well-fitting pack. Actually I am going to remove the sternum staps on my ULA, because the should straps fit me perfect. This is the challenge, to minimize sizes and cover a large range of body shapes/sizes. It might be easier to fix our economic woes, than to devise a small product line that adapts to many sizes of torsos!!
Hip pockets - I like them. For me, hip pockets are a requirement in a pack. The ULA pockets are removeable, but a little bit of work, because you have to undo the shoulder stap buckles. They weigh about 1 oz each. I love the ULA hip pockets. They are much bigger than the ones on my Gregory 95L. Brian's hip pockets are simply wonderful.
Question - I know you need to generate sales to stay in business. You have some great products, especially the Merino Hoody, which fills a unique niche in the market place. How is your pack going to fit into the market place? How is it different that the offerings from ULA, MLD, GoLit, 6 Moons, etc? Is is just a re-hash of what is already available. Please don't take these questions as a negative... but I would like to see something new and unique. The pack isn't that light, doesn't have anything already available somewhere else. So the last benefit you might offer is price. Can you sell it for $80 or less?... Probably not. I just bring these things up, because there is a cost to product R&D, and you must assess the market before investing in production. BTW, I have found this site and your book excellent resources, so I am a BPL fan... just to set the record straight.
Good luck on whatever path you choose, and it is a nice touch to see you solicit feedback from your readers.