>> the libraries you have come to depend on aren't there
See e.g. Inline::Perl5 and Inline::Python (don't know how mature that is).
>> For a new language to get adoption
I'm not really that knowledgeable right now, but how many weeks have Perl 6 (the language, not the libraries) had an implementation ready for production? :-)
Edit: Thanks, Ulti. Close to 50 weeks. Good work of the implementors. :-)