Interesting question.
I do extensive (up to 2-3 weeks far away from support) backpacking with 2 camera systems, tent, sleeping bag, and a lot of equipment and have yet to see a succesfull photobackpack design for the wilderness. The one that almost makes it there in my humble opinion is the large one from clikelite. Why almost? Because the harness system and the straps are not even close in comfort and load capacity to a real mountain/trekking backpack.
A lot of people would say: I don't need a huge backpack because my trekking is limited to 1 or 3 days, a basic photo backpack large enough to fit my camera and a couple of power bars should do the trick. Well, I'm totally opposed to that approach. I believe firmly in compact, solid survival kits even for shortest hikes.
Even for a day long trek, you'd need a first aid kit, an emergency blanket, an additional layer of cloth, food, etc. I'm not suggesting a huge 80 or 90 liters pack, but at least a solid 50-60 liters one with comfortable wide straps, great support system. For short treks I'd look for a mountain pack and use the sleeping back compartment for my equipment well packed in a padded photo bag and the main compartment for the trekking/camping equipment. I also carry a basic sleeping pad for every trek. It's extremely comfortable for composing close to the ground or for laying the equipment over it in wet grass or over snow.