Without another name change, I don’t think that phrase will ever go away, for the simple fact that X as a name is too short and nondescript. In speech, X could refer to a someone you broke up with, or it could just be the beginning of another word, serving as a prefix. In text, it could refer to the actual letter itself, or the close button on a window, or a placeholder, or something NSFW.
There’s simply too many ways that X can be interpreted that even if people associate Twitter with X, people will still specify “formerly Twitter” just to avoid confusion
That’s a misinterpretation of the poem. The point was that both paths were equally valid but no matter what he picked, he would always think that the other was better. It was a poem about “the grass is always greener on the other side”