I understand where you're coming from; however, the small nylon loop on the OpTech strap would easily fit the Leica SL flat lug. However however, I'm not sure about the weight-carrying capacity. IIRC, the SL is a fairly heavy piece of equipment, and certainly pricey enough that I wouldn't take any chances with it.
Once more, the problem is not to fit a strap through the lugs, it's in the strain that the lug exert on the strap since they are not turning like the usual rings on usual camera lugs. It's all explained in the article, and on Harry Benz's website (with a diagram too). Best regards,
Vieri