What does it matter what the UA does with the information? The point is that the information is supplied; the UA can provide whatever benefit from it that the user wants from it.
For example, I was just thinking that forum software could have their backends scrape image links you attempt to embed; and, if they find that the link has a sunset policy (e.g. it was from an anonymous image upload service that expires posts after a week), then they could rehost the image instead of hotlinking to it. (Or, cache the image for now, and then rewrite the link from a hotlink to a cached link when the deadline hits.)
That’s not something you would standardize behaviour on. But, once you have servers providing the information—not to a particular client, but just spewing it out as an objective fact out into the world—clients can do all sorts of things.
Standardisation does nothing for this. The software could've always just used an X-Sunset header or just another field in their dto.
My point was that there will never be a client that will blindly read that value and understand what to do with it. Which is why the only difference to "X-Sunset" is that there's an RFC with suggestions on how it could potentially be meant there, along with a syntax restriction.
ActivityPub is the epitome of this because they supply a lot of vocabulary and syntax variation to express them (including very complex ways to normalise that syntax, JSON-LD is not fun to parse) but doesn't actually made the implementation commit to anything. It's setting up a bunch of arbitrary rules for nothing. Every single AP implementation still orients itself on compatibility with Mastodon.
Sure it does. If the information is standardized then the community as a whole can innovate around it. Browser plugins and the like can be made that make use of the information, etc.
Or HTTP-based APIs could check for it and write out log entries or send out alerts to notify ops or the devs that they'll need to investigate further as to how this affects them.
For example, I was just thinking that forum software could have their backends scrape image links you attempt to embed; and, if they find that the link has a sunset policy (e.g. it was from an anonymous image upload service that expires posts after a week), then they could rehost the image instead of hotlinking to it. (Or, cache the image for now, and then rewrite the link from a hotlink to a cached link when the deadline hits.)
That’s not something you would standardize behaviour on. But, once you have servers providing the information—not to a particular client, but just spewing it out as an objective fact out into the world—clients can do all sorts of things.