I think you see lemon used on Fanfiction but not AO3. Lime pretty much died out as a term by the purges of 2012 and the rest of the "Citrus Scale" died before that.Whatever happened to those author notes that would appear in the middle of a chapter? The only solid example I can think of is My Immortal but I remember it being prevalent during around 2008-2011.
Also, do people still use the terms lemon, lime, grapefruit? I don't see them as often as I used to, never on AO3. Rarely on fanfiction.net.
Even then, the term "Lemon" isn't as commonly used as it used to be and you mostly see it come up in anime fics, since the Citrus Scale started in anime fanfics.
Nowadays, it's more likely to be in use among the older and less active fandoms where some of the writers from the fandom's heyday are still sort of active and post new stories with the term.