Component-level weight ratings are indeed lacking right now, although I will note that the author appears to be proposing a frame-only weight rating, presumably because while all other parts of a bike can be replaced, the frame is at the center of a bike, setting aside Ship of Theseus considerations. Replacing a frame is virtually equivalent to building a new bike, after all.

Of course, a manufacturer of assembled bikes should publish an overall weight limit for the bike as-assembled. But still, it might be nice to know that the frame specifically is overbuilt for that particular assemblage, meaning it has capacity that can be utilized with the appropriate upgrades.

You're absolutely right that just rating the frame alone won't necessarily result in broader marker supply, but it's certainly a start. As I said, there's a vicious feedback cycle and the way to break it is to find a niche and grow it. Perhaps mandating a frame-only weight rating will spur lawyers to require all weight-bearing components to also have weight ratings as legal cover, or something like that. Such a limit might be low, though, but is still progress.