I may be misunderstanding your comments, but it sounds like you are looking for a rig that is similar to some backpacking systems, where the weight of the pack while hiking is supported by the hips, rather than the shoulders. It would seem that this shouldnt be a particular issue for a scuba harness since, in the water, you are horizontal (for the most part) and weight distribution, other than for trim, shouldnt be a primary concern. (Yes, carrying BM doubles on land, if you have a significant distance to travel between car and dive site, might be a concern.)
You're right, that's a big concern cus I'm not a big guy. Balancing 3-4 tanks while doing a beach entry on slippery round rocks at places like Bali ain't easy. I prefer to put as much of the load around the hips instead of being high up. That and a recent knee surgery has me looking around for alternatives to not f%#k up my knees anymore.
You are experiencing one of the exciting things (for me at least) about the current state of sidemount equipment development. While the rapid introduction of commercial SM rigs (Nomad, Razor, RECON, Armadillo, PROFILE, etc) has increased the accessibility of SM to a broader audience of divers, the development is in some ways still in its adolescence, and there is a lot of appeal to gearheads (I say that positively, as I fear I am one) people who want to tweak their set up, refine it, experiment with it, etc. I did a presentation on sidemount diving last night to our scuba club, and had a conversation afterward with a member who is a very enthusiastic vintage equipment diver, about the similarities between vintage and SM in this regard. For the vintage folks, a bit of engineering goes on, because parts and specific equipment may no longer be commercially available. For SM, a bit of engineering goes on, because what is available may not suit everyone and it is fun to try different alterations. So, we benefit from the years/decades of tweaking and refining that people like Lamar Hines and Steve Bogaerts have done on their own gear, but still find ways to try and improve commercial rigs to meet our own individual needs.
You & I too, it feels more like an incurable disease for gear heads like us. I haven't even done a single sm & I'm already trying to reinvent the wheel. I've even done some cad drawings of the weight support components of my ideal sm rig.
SangP