> I honestly can't name any other ecosystem where you can just jump in and all these problems are already solved for you by the core project maintainers

I'm on the Dart team. We ship the SDK with a native VM, dart->js compiler, set of core libraries, package manager, and build system. There are canonical packages managed by the team for unittesting (using a Jasmine-style API) and logging.

I do have to admit the logging stuff isn't that baked, but the rest of the pieces are heavily used and have a lot of community-wide mindshare.

Not that I'm trying to steal any of Elixir's thunder here. I'm continually impressed by how polished everything they do looks. As someone who went through a language's 1.0 announcement, I really like how they clearly listed their compatibility expectations going forward.