Well let me at least leave why I think Nix is not it at the moment:

• Software Center - browsing search.nixos.org isn't quite the same in terms low friction and discoverability
  • You already have to know what you're looking for, and it can't make system config on your behalf
  • Debian or conventional package managers usually offer a native GUI for package selection and deployment
• System Defaults - the minimality of a basic default install can cause a lot of papercuts
  • the default boot partition is rather small given the OS's prepecity to add new kernels with new generations
  • and without any garbage collection service enabled by default, user first encounter switch failures due to this
• External Binaries Compatibility - Linux also suffers from this in general as compared to MacOS or Windows
  • in addition to being much more niche, reuse of existing binaries from more prevalent distros becomes complicated
  • the desktop ISO could suggest a nix-ld config with default libs most binary distributes expect, easing in new users
• The Nix language - much more complex than conventional cong markup langs, being more of a turing complete DSL
  • partial working LSP impare introspection while writing, and the runtime error messages are poorly formatted
  • most desktop users (in debian or fedora) have little need to learn their OS's packaging schemas, but NixOS users do