"Projects such as GNU Guix or Nix solve the problems quite nicely, IMO."
So long as you define the problem space as "package management for POSIX systems," and in the case of Guix you can scratch OS X and I think the BSDs off the list, too. If your package manager doesn't run on all of Windows, Linux and OS X at a bare minimum then your package manager is not solving the problems of Node.js, Python, PHP, Perl, Ruby or any other cross-platform runtime.
Sigh. Well fine, if you're stuck on Windows then language-specific package managers are much better than nothing. But on POSIX systems, we can do so much better than the current mess.
So long as you define the problem space as "package management for POSIX systems," and in the case of Guix you can scratch OS X and I think the BSDs off the list, too. If your package manager doesn't run on all of Windows, Linux and OS X at a bare minimum then your package manager is not solving the problems of Node.js, Python, PHP, Perl, Ruby or any other cross-platform runtime.