I believe there are two different issues. The first is what is the maximum possible number of articles (this is what I asked). For all practical purposes (manpower we have, time until Wikipedia will collapce and cease to exist, etc) we will only able to write a tiny part of them. This is why media are discussing questions like whether English Wikipedia will ever reach 5M articles. I think this is a much more complex issue which has to do with the editor retention dynamics and general lifetime of internet companies.