My estimate is based on CPAN, which, in the early 2000s, was already lauded for offering an extensive, high-quality ecosystem despite having "just" 20,000 packages (contrast modern NPM, which claims >500k). Hence I consider this the lower bound of an ecosystem which can be reasonably expected to provide foundations, if not pre-made solutions, for anything you might expect to do in the course of general purpose programming. And it seems reasonable to assume that one maintainer per package is enough to sustain such a system.

Clojure hit 20,000 recently according to clojars.org . So that's it - we're where Perl was in 2001. Makes me feel all fuzzy inside as Perl was my first love.