Interesting idea. Hope someone chimes in. I've never liked the HPG harness, but considering how many love it, I've always assumed I'm using it wrong in some way.
The HPG does a good job laying well mostly because it is so thin and pliable, however, I would suspect most would prefer our harness for any real load carriage.
I experimented with the HPG harness years and years ago. I had a Tarahumara that I liked it with. On a system like ours though it gets really floppy and is a pain to get in and out of. Not worth the hassle.