good concept. though to be honest you want the mags as close to your front more then on your back or sides. makes for easier reloading during combat situations. that is why we have our magazine pouches on the front of our IOTVs and IBAs.
jap good point...depending a bit on how far we set this in the future, imho it´s imaginable that all these components are so miniaturized to fit in a small backpack(maybe integrated into the armor itself)...lightweight armor material overrides the weight problem (and thats only a question of time until they come up with some high tech super polymer whatever stuff that stop bullets and weighs only a fraction of todays ceramic plates)