Linux

I don't know how Manjaro plans to do it, but Universal Blue distros have access to the entire set of dnf repositories, including non-free packages. You run rpm-ostree install, and it layers the package you want. Each system update re-layers the custom package layer after upgrading the system layer.

But since this is pre-alphaware, it's kind of early to be passing judgement on how/if they'll have access to the AUR and whether you could layer packages. Seems like the "safety" aspect is served through having an immutable system, which ensures end users have the same base as everyone else.

And it's fine if that's not your cup of tea. Sounds like it's not. Arch, openSUSE, Debian, and their mutable descendants aren't going anywhere.