I think we need at least one "constructed languages" tag. Maybe even a specific one like Volapük. Esperanto is a constructed language and because of that, our history is interrelated with that of other constructed languages. Sometimes it makes sense to compare and contrast with these languages. What do you think, do we need this tag?
I think this might tie into my proposal to have a tag for each language for when a question makes a reference to it. I don't see why we couldn't make a Volapük tag in a similar way.
A tag for constructed languages in general for when a question compares Esperanto to all other constructed languages seems reasonable to me. This makes perfect sense for example in this question comparing numbers of speakers.