I'm not a unix guru, but from my experience with C++ build systems I feel the reproducible build thing seems completely at odds with rolling releases. When I have a reproducible built with C++/CMake/Hunter, what I want is a stable package base that everyone is building against - that's got a ton of eyeballs on it and that is patched and maintained. You do whatever you want on top of that and you can deterministically reproduce your whole stable setup. You do it all carefully enough and you can even build against any architecture.

You take the example of Ubuntu LTS - everyone eventually adjusts their libraries and applications to be able to run with the suite of library versions they provide and everyone is on the same page.

Sure, sometimes you may need a particular package at a different version. You can either static link that in, or bring it in separately with a PPA (as long as you're careful to not link two versions of the same library) - but generally that's not really necessary

By contrast a rolling release seems sorta nuts... Sure I can reproduce the GUIX/NIX package world at some random point in the past - but I'll be basically the only person stuck at that version. If libraries have issues all I can do it try to rebuild at a newer version.. but then why do I care about reproducibility if I'm rolling? Or I end up with a hodge-podge of libraries at different versiosn that work for one application, but don't quite work for another. Orrrr I have a soup of libraries/dependencies all at different version.. but then I might as well statically link everything and forget about package management!

From a lot of the blog posts and tooling I get the sense that people don't really care about having a stable system frozen in time. Is that right?

I admittedly haven't played with either system (b/c they're really hard to grok) - but I feel I must be missing the point a bit. Or maybe I'm not seeing an obvious usecase for reproducible rolling releases