How is Nyxt? I've been meaning to try it out. Is it usable for day-to-day tasks? What are the remaining 30% of your use?
As for Guix, I've approached it twice, both times installing (what was then known as) GuixSD. Couldn't really make it work. What are your experiences? And your configuration? :).
Emacs, that I swear by.
Still, what's missing in this picture, and why I mentioned PowerShell, is a typed integration with entire OS. Operating on objects / typed data, invoking functions - instead of passing unstructured blobs of text around. That's what I like about PowerShell approach - my scripts don't invoke CLI utilities, they ask system for objects, inspect them, call into their methods. This is similar to the Lisp Machines, where you could code against objects representing your OS runtime state.
If we could somehow bolt that on top - replace existing Unix tools with ones accepting and producing structured data (or even wrap them) - then the picture would be complete. And I wouldn't mind using four different Lisps, if that's what it takes :).