You're misunderstanding, and it's a great opportunity for me to clarify:

I want a graphical installer for applications within NixOS.

Currently NixOS applications are added by editing the configuration.nix, with more specific tooling avaliable via flakes and home-manager. We agree that this is cool and good.

What I want for consumer use is NixOS, with an interal graphical installer that handles updating configurations in the background; ideally forming a no-terminal-necessary UX for consumer users.

Ah, yes, I see now. I think a NixOS configuration is best managed as text, but I can see now how code generation could potentially bridge that gap. I'm not currently confident in the ability of LLMs to do this, but I do think that a kind of "NixOS IDE", perhaps with a some GUI elements and writing to some constrained files is a good idea.

Once upon a time, Snowflake OS was working on this, but I don't think the project is very active anymore.