Normally you'd just be using one glibc version. Packages that you installed a while ago may be using a different one, but it's not like every package has massiv

Normally you'd just be using one glibc version. Packages that you installed a while ago may be using a different one, but it's not like every package has massively divergent dependencies. Because of the immutable store, you can do file level deduplication, so if you have multiple versions of the same packages, you can deduplicate the identical files. I think the worries about disk usage are relevant, but only on systems with small amounts of storage. These are still relevant though, and it's an important area to improve on. As for burning CPU time, I don't think there's a perfect solution to avoid this, but I think Guix is pretty good. Guix provides substitutes, so you don't have to build things locally on every machine (I'm looking at you Rubygems, pip and Python stuff is pretty bad also).