Dear people, neither Klingon nor LFN have any native speakers. Okay, that's not entirely true. There has been a case of a certain D'Armond Speers who tried to raise his son in Klingon (thus making him the one and only native speaker), but it was not a success because the language lacked elementary words like "table". The only artificial language that has ever had more than one native speaker is Esperanto (not counting semi-artificial reconstructions like Rumantsch Grischun, Modern Hebrew etc.).
And this is precisely where we are getting to the issue brought in by MF-Warburg: "Can we, by the way, define more detailed criteria for which artificial languages should be eligible?"
My point of view is that there are two main criteria here:
a) Is the language developed enough to make such a project possible at all?
b) Is the community of people willing to work on the project large enough to make it viable?
One might also add as a third criterion:
c) Is the language intended/suitable for human communication at all?
Klingon has a large fan base, but it fails the criteria a en c. The same goes also for proposed projects in Tolkien's Quenya and Sindarin.
Another interesting case in point is Toki Pona, which used to have a Wikipedia in the past, but it was deleted, apparently because it was practically empty. The language seems to be quite popular, but the community clearly was too small to make it a success. Besides, I'm not sure how the idea of a language with only ±120 words can really work well for an encyclopedia.
But when a language fulfills all three criteria, I cannot see why a project shouldn't be given a chance. The Wikipedias in Esperanto, Interlingua and Ido are doing reasonably well. Those in Volapük and Occidental/Interlingue to some degree as well. The projects in Lojban and Novial are practically dead.
Cheers,
Jan