Many of us know that the numbers usually cited for the amount of Esperanto speakers is an estimate, and a rather old estimate by now that seems to circulate mainly because everyone repeats it over and over because it matches our gut feelings and vague impressions well enough (as we see on the current Wikipedia page for Esperanto, I see the common range of "between 100,000 and 10 million L2 speakers".)
I intend to differentiate my question from this one: How many Esperanto speakers exist? by asking: We know it's difficult to calculate the real number, so do we have any ideas for how it might one day be done?
The reasons for why it is difficult are clear. It's hard to calculate the "speakers" of any language (and we must first define "speaker"), let alone a language like Esperanto, which is not one of the "larger" world languages, and whose speakers are not concentrated in any particular region.
A starting place for exploring our attempts and successes/failures at calculating Esperanto speakers is here: Statistiko de Esperantujo.
Perhaps this is a question better directed towards specialists in the field of demographics or statistics, but I want to begin asking this question somewhere. And perhaps it's too theoretical, or too discussion-y and not question-y enough. And if my question isn't different enough from "How many Esperanto speakers exist?", I understand. But this is a lingering question in the Esperanto community, and finding a solution would be a great achievement.
Edit: IMO this answer by Marcos Cramer is worth reading (as are all of the answers to "How many Esperanto speakers exist?", but this one particularly) before discussing this topic: