URIs are pretty much immutable. My impression is that what the OP suggests is a guaranteed lifetime of the content associated with the URI. As for this second

URIs are pretty much immutable. My impression is that what the OP suggests is a guaranteed lifetime of the content associated with the URI. As for this second part, "once it's published it should always remain out there", I'm not very sure it's a good idea. In many cases I'd actually like to be able to say that a piece of content has expired (the content is not relevant anymore).