...getting people to agree on a good common core language is a good thing even if the language supports namespaces.
That's a good point. ^_^ I don't use Anarki- or Lathe-specific stuff in my examples if I can help it. And I recently mused on the trend for a language to incorporate a lot of features in the standard so as to improve the common ground, so I should have seen that point to begin with.
Namespaces solve the problem flawlessly only if you plan for no one to work on or read anyone else's code, ever.
I've sorta been banking on the idea that everyone programs to their own languages of utilities anyway, and that each of those languages can be talked about, accepted as a common topic, promoted by its proponents, and standardized just like language cores can. Certainly CMSes and game engines have those kinds of communities. :)
Multiple independently developed libraries won't always work together well enough to all be clearly canon components of the language's identity, but I think they are more likely to be interoperable than are things designed from the outset to be entirely new languages. So I don't think it's important for the core libraries to be cutting-edge in practice. The core can fade into the background to a degree.
I haven't thought about this stuff very deeply yet, and it's not rooted in a lot of fact, so please feel free to disillusion me. ^^
 I don't mean to suggest there's a well-ordered expected value of interoperability. Whether a library is designed or used in an interoperable or impregnable way is sorta relative and idiosyncratic. One more avenue for interoperability could even be annoying if people come to depend on it in poorly prepared-for ways. ^_^