Dear Tomas M,
Over the last year i have been using my custom linux-live script to make distro just by using the squashfs files from standard live cd. Like ripping xubuntu squashfs filesystem.squashfs file and renaming it to 000-xubunutu-$
ver.sb or something like that. My script uses overlayfs and is very stable. I know it's stable because I have had these live systems running for 10+ days. The only 'problem' maybe thunar doesn't see is the size of a folder. (As in the folder will say 0 bytes in overlayfs union. This only is a problem with Thuar though. I also this problem is fix in xubuntu 20.10.)
My scripts have aufs support also but you have to add aufs=y to the boot command line. Overlayfs is the default cause that will be in nearly every distro vs aufs. I also noticed aufs being unstable in kernel 5.8+ for some reason.
Main point:
I think a possible future for linux-live/slax is to be used as a set of scripts made to work with nearly any distro as it is. Anyways I hope this helps.