That's irrelevant. My whole point is that such restrictions go against the whole design of the PKI, at a systemic level. It's actively harmful to try to restrict trust in a CA to certificates for a certain TLD, because the two don't have any relationship whatsoever, by design.

It would be like restricting trust in a CA to certificates for sites whose name starts with a certain letter. It's exactly as meaningful from a Web PKI perspective.

Could Microsoft make it so that Windows only trusts this CA for certificates on domains whose name starts with a "b"? Sure. Would it help with anything? No. Would it be actively harmful to companies whose name starts with A that are using this CA? Yes. The same thing is true for domains whose name ends in .br.