Yes, DMARC isn't solving the same problem — but DMARC is showing how the category of PSL problems can be solved with DNS. With HTTP/3 now fully expecting browsers to be able to benefit from transparent-upgrade record responses, i.e. `www IN HTTPS 1 . alpn="h3,h2"`, then it is possible for the style of solution shown by DMARC to be applied to other problems that PSL solves today.

CAA isn't a good fit as-is either, because the subdomain has top precedence over the parent domain — precisely the inverse relationship needed here. But having worked with the PSL for quite some time operationally and seeing the direction of trends away from it and towards structural DNS declarations rather than a centralized list, I think the 3LD-2LD-CRSF problem would be far better off solved with DNS than PSL.

Basically, just adding `co.uk. IN TLD subs=independent` as an SVCB record would fully deprecate the need for the PSL versus cross-site and other such ownership-changes-hands boundary problems with both A.co.uk being allowed cross-site with B.co.uk, and with co.uk being treated as equivalent to B.co.uk by password managers, cookie repositories, and so on. It would also benefit CAA by defining whether the boundary exists — if TLS is hosted by the provider, then any CAA records published by the subdomain should be disregarded; if the subdomains are fully independent, then any CAA records published by the parent should be disregarded — which simply isn't possible today without either referring to the PSL or implementing DMARC-style DNS solutions.

(I don't formally suggest that exact record as structured or written but it's sufficient a napkin sketch of what I mean by gesturing at that RFC to be considered.)