I've often thought this was a good idea. Personally I'd like to see a belt order, that the "beaver tail" or whatever would just slip behind, so you don't lose any space on the rear of the belt. The pack would then sit on top of the rear pouches. I think this works up to about 50 lbs or so. After that, you need a padded hip belt such as this, and just eat the lost space on the belt, unless, you cobble something up where the lower section of the pack stays on the belt line, when jettisoning the top portion. The "beaver tail" as it were could still fit into a slot between "buttpack" and belt.
If you could figure this all out, you'd have the perfect system for the grunt. Oh and a nice curved framesheet so your rear plate doesn't slide around.
Love the Auscam!