CSSWG is considering changing the spec to avoid confusing for CJK developers, see https://github.com/w3c/csswg-drafts/issues/7577. Sorry I didn't pay attention to this feature earlier, I hope it's not too late to change a shipped/near shipping feature.
This is not behind the flag so hmm. It would be easy enough to just switch out the previous character for the new one, but I wonder if there're any implications.
IIRC (because I don't have any Apple devices to test on), this has already been shipped since macOS Monterey 12.3