It does smell very much like a feature that is currently implemented as a text file but will eventually need to grow to its own protocol, like, indeed, the hostfile becoming DNS.

One key difference between this list and standard DNS (at least as I understand it; maybe they added an extension to DNS I haven't seen) is the list requires independent attestation. You can't trust `foo.com` to just list its subdomains; that would be a trivial attack vector for a malware distributor to say "Oh hey, yeah, trustme.com is a public suffix; you shouldn't treat its subdomains as the same thing" and then spin up malware1.trustme.com, malware2.trustme.com, etc. Domain owners can't be the sole arbiter of whether their domain counts as a "public suffix" from the point of view of user safety.