Well kind of what you are looking for can be achieved with Kifaru Marauder pack. You open it up by unzipping a front panel (like a suitcase) which allows you to see the entire inside of the pack. Since there is mole webbing inside you can attach pockets and pouches also made by Kifaru and organize your gear. Since pack has also molle webbing on the outside you can also attach pouches there in order to make it bigger. Using all the pouches makes it for a heavier set up but it sure keeps things organized.

You can see pouches inside the pack for gear organization (http://brunerdog.tripod.com/images/usn/m3.jpg):


This view shows you how I added more storage space on the outside of the pack. The back pouch and claymore pouch gave me additional storage and if I wanted to I could have attached two extra pouches on the left and right side (http://brunerdog.tripod.com/images/usn/m1.jpg).


Annother option is a Kifaru Xray that is a top loading/front pannel hybrid. You can load stuff from the top but also you can open up a front pannel on the bottom. Also this pack can be customized with additional pockets and pouches.

This is a pack with extra pouches:


And this is what I meant by front/top loader hybrid:


And this is size comparison: