I haven't dug into Guix yet, so is the config more of a markup and less of Turing complete language? That sounds like it'd be easier to grock or optimize an LSP for.
I have heard that Guix takes a stronger stance with respect to unfree software. I don't think any of the official nix Hydra infrastructures build for unfree packages, but they are packaged and indexed into nixpkgs. Has Guix been difficult at all in that regard, i.e. using proprietary drivers or closed libraries for work or personal hardware?
That is a bizarre looking error. What architecture is your host system? Is your config repo publicly viewable? Installing tail scale is your only build issue?