Assuming a domain name as a hard boundary for information is a disaster, imho. All of our fights over "1st party" and "3rd party" based on arbitrary names for a service is just specious, and the continued emphasis of "origin" as a "load-bearing" pillar is only due to legacy, not due to utility. The First Party Set proposal reflects a real need of enterprises and services, though the edge cases of the current solution, and complaints about the proposal, really reflect the competing demands of those who want freeflow of information vs. those fearing an expansion of the privacy violations bad actors have created. Because these extremes exist, these edge cases, the whole proposal should get shut down?

We've evolved into this silliness. Even as we see domains fading from view (address bars are really just search bars, who actually types a full domain anymore?), we are now forced to have multiple domains to reflect "relevance" of our content, thanks to SEO, naming conventions, etc. A company may have 6-10 domains, some reflecting regional customs, some reflecting a specific content focus, and some for specific segments of their customer base. While no company or publisher really _wants_ to manage all these domains (and certificates and payments), it's often forced by external requirements. First Party Sets nicely solved for some of these problems, by allowing entities to treat these various names as one surface for their own use, while still restricting external entities from access in client, allowing SEO to function as expected, etc.

Yes, some companies have managed to keep almost everything under one domain (apple.com), and some appear to not worry about how many domains they manage, as they all seem to get search relevance and share information (google.com)... but in the real world, we are now in a place where, at a certain scale, multiple domains are often helpful, and in some cases, necessary.

The First Party Sets proposal gave companies the ability to treat their interactions consistently no matter the domain name, which is exactly what any user would expect, and it also protected privacy, by revealing that multiple entities are under one roof (in case you didn't know that Verizon owns AOL sites like TechCrunch). Users shouldn't have to care what domain name they are on, it's the entity that matters, both for good (happy to not have to login AGAIN) and bad (What? These jerks control this site? I'm outta here!).

The comments in the proposal highlight some edge cases where bad actors could permeate privacy protections, but a) they are solvable with revisions, and b) highlight the bluntness of many of our current attempts at privacy protection via "domains".

I expect some aspect of "cross-domain" entity identification will continue to be proposed, and I expect the browsers will add it, even if W3C doesn't accept it as a standard. This corner we've created has some benefits, and controls on rampant data-spewing are welcome. But we don't need to keep building on every legacy aspect of the web: Flash is gone. We don't use the <blink> tag. We don't use RealAudio for streaming anymore. And we don't need to assume that a domain should be a boundary for the entity owning it.

(minor edit: I really need to do better with where I put commas)