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I think that the cinch might be the best single strap out there, but I don't like to have too much duplication or incompatibility between accessories, so if there were a way to deploy double cinches when needed, that could be a big help.
I had two separate thoughts about modifying them for that purpose, but I don't think I explained myself very well. Both would take advantage of the modularity of the strap though.
The first is very simple, just clip the two D-rings together at the back, either with a piece of webbing or a heavy duty Velcro tie-down. It would look like an X from the back, but the straps wouldn't actually overlap. Would have to see how this behaves when moving either camera up to the eye. They're essentially being worn as two separate over the shoulder straps, not cross body, the clip simply keeps them from falling off the shoulder.
The other idea could be employed on either a single strap or two, again without actually crossing them. In this case, however, we make greater use of the modularity of the strap. We remove all the webbing and the cinch glides. We're not going to use the webbing, but we are going to re-use the cinch glides by threading one continuous piece of webbing through the connector at each end and attaching them to the shoulder pad. Strap would remain adjustable front and back, but you would have to employ a swivel connector from another make to ride the loop. Either of BR, carryspeed or sunbounce. This would basically turn the cinch from a double point sling to a single point slider, more like the original loop, albeit a highly adjustable one.
My reasons for wanting to tinker so much are manifold. I think the two point sling is better for some camera+lens applications while the slider is better for others. As of yet there really isn't a product that offers flexibility in a low profile package. The double straps for Black Rapid, Sunbounce, and CarrySpeed especially, are just too bulky and paramilitary looking, especially across the chest. Holdfast's Moneymaker has an appropriate slim profile, but no cinching capability and is not separable for single camera carry - still very attractive. Optech also had a dual sling that doesn't encumber the chest or look like over padded swat gear, but it has other limitations.