I have been designing a stand up fighting station for use form the beach. Basically it involves a square piece of metal welded to the bottom of a metal pole. The idea being that you bury the metal base in the sand to cement it into place and then at the top of the pole is a fully swiveling rod holder that has the ability to bend forwards and backwards (with a stopping point going forward that can be altered with a pin). Essentially you would have a stand up fighting chair. This would allow you to use max drag on large sharks without being pulled into the water or being spooled because you cant handle the higher drag. Obviously the rod could be removed at any time if necessary but a lot of the fighting could be dont from this station. I know the description is a bit rough but is this something that you guys could be being a positive addition to your fishing arsenal?
sounds like more shit to lug out on the beach. 
I've seen guys use pvc as a gimbal type deal so your idea could work. but honestly, I've been hooked up with over 60lbs of drag and not needed a harness or chair, just a gimbal belt, and i think most here would rather go mono e mono with the fish and lose then have spiffy gadgets and winches and land them.
sounds like you put some thought into this. safety always a good thing. with my fighting belt i can hook the pole to the belt and put a tether on the back of the belt, that can be hooked to a anchor point. I use a dog run tie down that screws into the ground. works great