Since this is a fairly custom task, I would approach it with a custom
solution.
- GPT
- systemd-boot
- One /boot partition
- One BTRFS-on-LUKS partition (formatted using the distro with the
oldest kernel)
- {@root,@home,@var,@srv,@opt}-{distro1,distro2,distro3} subvolumes
- Potentially {@distro1,distro2,distro3}-{downloads,documents,pictures}
subvolumes, if there's a usecase for that
- Bootstrap all the distros manually. Arch and Gentoo do that by
default, debian land has debootstrap, not too familiar with rhel
universe, but at the end of the day everything's a file :)
You could also write a script that keeps all the distros up to date
from within whichever one you're currently booted by mounting
subvolumes to /mnt or wherever, chrooting in and running the update.
You could also replace systemd-boot with efibootmgr to use UEFI boot
directly, but I would advise doing that after the everything is working
correctly as it's much easier to experiment using a good old bootloader
edit function.
BTRFS requires _some_ maintenance, but imho it's reasonable - run a
deduplication and defrag job on a scheduling tool of your choice and
you're good to go!
$0.02
