Even though I am a big Emacs head, I have not. It does look pretty cool though. I'll have to try it someday. Ultimately I ended up on Gentoo. It lands in a similar niche in terms of being a meta-distribution, but it does not take a declarative approach to configuration. The biggest drawback of Gentoo in comparison to NixOS / Guix is that it isn't able to cache a vast array of package configurations the way NixOS does. Everything needs to be compiled, whereas on NixOS you can flip one switch and instantly get a package that was compiled with different build-time options / dependencies.