An ancient proposal for stable IDs were Tag URIs [RFC 4151]: URIs which still have an understandable identifier like a domain but with a date encoded at the time of minting the URI which keeps the URI "valid" even if the domain lapses and minting "authority" moves to someone different.
tag:chrismorgan.info,2019-01-01:blog/slug
But the real problem, of course, is people caring: You'll need to store the ID with the content and continue using them when moving CMSs or domains. People, apart from your notable exception, don’t do that.
(Sorry for minting an example tag URI in your authority! I shouldn’t have done that according to the RFC.)
tag:chrismorgan.info,2019-01-01:blog/slug
But the real problem, of course, is people caring: You'll need to store the ID with the content and continue using them when moving CMSs or domains. People, apart from your notable exception, don’t do that.
(Sorry for minting an example tag URI in your authority! I shouldn’t have done that according to the RFC.)
[RFC 4151] https://www.rfc-editor.org/rfc/rfc4151.html