NixOS and GuixSD aren't user friendly because the people who use them are like GNU/Linux users circa 2000: people insane enough to install an operating system that is very particular about who its friends are.

But they do have an excellent solution to the whole updates debacle: Install them in a separate location, initialise them when booting or when they're finished installing, and delete them when they're inaccessible from a few standard locations like /boot or /proc.