Disclaimer: I haven&#x27;t ever used Guix, but I&#x27;ve used NixOS which builds on the same roots.<p>Typically your total system-configuration can be divided into a few distinct parts: bootloader and filesystem-partitions, kernel and software.<p>These features are to some extent dependent on each other, but not in any way which breaks dependency management or causes conflict, and thus can mostly be treated distinctly.<p>Basically you configure A bootloader, not several. The configuration is about which one that is and where you put it. Depending on if you use UEFI or not, this is either 100% tied to the filesystem layout, or just 99%.<p>Then the rest of the tooling just uses that info to populate the boot menu. In functional terms, a bootloader should have no side-effects on the system booted, so as long it boots the system, you should be fine.<p>The kernel doesn&#x27;t really care about what bootloader you use as, as long as it boots it with the correct parameters. You can have several kernel-configurations in parallell which are accessible from the same bootloader-menu, but as you say, you cannot be booted into several versions at the same time.<p>That&#x27;s not really a real-world problem though, because software very rarely depend on a specific kernel-version, they just depend on having <i>a</i> kernel. If a package depends on specific kernel modules, it&#x27;s free to add these as dependencies, which will be resolved.<p>This means you can have a 100% functionally constructed system on top of a few config-files, with minimal chance of crafting a configuration which is internally incompatible. If it is, the tooling will tell you, and your system build will fail.<p>You can also have several mututally incompatible configurations within the same filesystem and boot between or chroot into these. It&#x27;s an incredibly powerful concept.<p>The only reason I&#x27;m not running NixOS today on my laptop is that I need 100% end-user finish with regard to a &quot;just works&quot; desktop, and I&#x27;m not willing to build that myself, one package at a time, with the limited spare-time I have.<p>So I appreciate and respect both NixOS and GUIX and the work being invested in them, but for now I run Fedora :)