Referring to a post on "Lemmy" or "kbin" is like saying you saw a post on your Windows or Mac computer.
That's not how language works. Language evolves naturally and in this scenario people would instantly know that the user had seen something on a fediverse platform without having to use another awful '-verse' word.
Likewise you can't police how people use language. People use whatever makes understanding for both sides easiest on both sides
If someone logs into a website called Kbin and sees something interesting, it's fair to say 'I saw something interesting on Kbin' without having to give unnecessary explanations about what the fediverse is.
And once again, no one likes the word fediverse...