A question: Is it possible to replace broken plastic D-rings with a metal carabiner? Or perhaps, insert a metal carabiner into the same slot as the D-ring and use the carabiner instead?
It is an idea I have but of course it may not be suitable for various reasons.
some of the advantages of D-rings and why people don't use other shape types (e.g O shape ones):
the way it's typicall attached with the curve portion allow multiple clip on & clip off (equipment, camera, stage bottles etc), w/o edges, snags...
the way weight is loaded up the D-ring with the flatter portion into the webbing distributes it more evenly so this has a bearing on the load spread as well as how webbing is affect (chaffing, poking)..