I plan on a LOT of hiking for nature shooting...
This might not be up your lane but my plan is going to be "modding" a bag. When I was in the civilian world I was a network admin and carried a REI Halfdome 3-day bag. If you are not familiar with hiking, 3-day bag may seam big but it is not. I loved that bag, used it for 10-years. It is water proof NICE padded back. Carried a laptop, test gear, 3-ring binder, change of shoes, and lunch. They don't make it anymore but I will plan on something similar.
Now the fun part, with my military time, sometimes we have to mod our gear. If you have a clear idea of what you want, any good shoe repair shop can do it. I plan on taking a holster style camera case and have it mounted on the inside on the back near the top. Then I will take a padded lens case and have it mounted to one side on the inside. It will be a large lens case so I don't have to worry about what size lens I carry. Most of these bags have a pouch mounted to the top and front, so the top will carry camera "kit." I know this part won't go for you but the snug straps on the outside will hold my tripod/mono pod.
I'm thinking something like this http://www.rei.com/product/778463/rei-lookout-40-pack
Hope this gives you an out of the box idea. You will be amazed at what a little ingenuity comes up with.