@phnt Guile and Scheme are hardly esoteric. (If they are to you, then whatever institute you studied at failed you.)
And it solves a real problem, I already mentioned the issue of Gentoo and power stability where I live.
Immutable distributions do solve the issue of interrupted upgrades. (UPSes also fail eventually. Designing the software so it's always tolerant is the way to go.)
Functional package managers are also more convenient to mess around in multiple namespaces & ephemeral environments with. (A bit like Qubes without the massive overhead.)