I think you will need to go to a cottage manufacturer as suggested. I've been through a bunch of the UL travel packs over the years and water bottle pockets were on the top of my list. The biggest problem was sizing, where the straps and the pack itself were okay for a smaller person, but not even close for anyone wearing an XL top. All the really light ones don't have water bottle pockets. The Sea to Summit Ultra Sil pack is a good example: it is light, but carries poorly, and has no pockets.
A work around to adding a water bottle to a SUL pack is to use a sling to carry the water. That gets the weight off the limited pack suspension and you can use them together or separately. Not as slick and clean, but something I considered. The sling option works with SUL waist packs too, again removing the weight and bulk of the water bottle.
I would love to see the classic rucksack design done in Cuben. A simple teardrop shape with drawstring top and two mesh pockets on the back. Get is sized so the bottom drops into the small of your back and you don't even know it's there. Leave out a back pad panel and it would roll to stash in your luggage. REI cranked them out for years and I would like to see a modern update.
Patagonia's Lightweight Travel pack has good ergonomics, but it is 11oz-- way over your request. Once you have gone down that path, the Cilogear 20L WorkSack is an interesting option, with great durability. I agree that the REI Stuff Travel Pack has great potential.
Personally, I've found that a small messenger style shoulder bag is better than a small backpack, particularly for travel. The Patagonia Travel Courier is a good example, 1037ci/17l and 7.1oz. You want something that is soft and will wrap around your hip. I just did a road/city trip and used a small Timbuk2 bag that is roughly 13x9x6 (702ci or 11.5L) and it was perfect for day tripping, but no water bottle pocket. Timbuk2 has UL Hidden Messenger model that is perfect except for the water bottle pocket issue. These bags are great for camera/phone/map/jacket/umbrella, etc. They are handy to increase carry-on capacity getting on a plane with a maximum sized backpack too.