The oldest instance of it that I know is putting something like download before or after the youtube domain. This must have been 2008±2. I very much doubt that's the first instance ever but I wasn't around online in the 90s (aside from on my grandma's machine who didn't know her computer had a web browser, but that wasn't very conscious, just a neutral net (young me) clicking buttons to see the effect)
It works well with bookmarklets. This swizzles between arxiv.org <-> www.talk2arxiv.org. I've now added it to my Favorites bar, next to arxiv.org/abs <-> arxiv.org/pdf and twitter.org <-> nitter.net. Thanks for the service!
It bugs me cause it's kinda true but kinda misleading, I don't know if casual web users realize it's a whole different domain. Sometimes it's not important, sometimes it is.
And where does this mention a constant mutation of urls as a mnemonic system as a substitute for a form submission to provide a service in 1-1 correspondence to another service?