Esperanto and other constructed languages are special cases compared to the way we usually categorize languages. Note that the only population we report is for L2 users of the language. And as a constructed language, though there are many enthusiasts, there is no population that could be considered to be an ethnic group that associates its primary identity with the language--at least not in the same way or to the same degree as we would expect for a heritage natural language.
Generally, we would consider a language to be EGIDS 4 if there is institutionally-supported use of the language in education. Can anyone tell us if that exists for Esperanto? That is, is Esperanto being taught as a first language of literacy acquisition for any sub-group of the user population? The literature that exists is primarily translated material (though without doubt there is some original literature being produced as well) but all of the literature is produced by L2 users of the language (almost by definition).
Can any Ethnologue user who is familiar with Esperanto add to our information on this?
EGIDS 6a does not seem right here. There is definitely a literature in the language and new titles are appearing. It would be good if the Language Development comment said something that reflected active literature production.
There are poems, novels, magazines and reviews, translations of literary works, songs, textbooks, anthologies, etc. in Esperanto [epo] as well as dictionaries and grammars. There is definitely a wide body of literature in this language, which would move the EGIDS value to 5. We will update this information on Esperanto in the 18th edition to be released in 2015.