tell me if this is what I’m looking for. I build Lineage OS, which requires me to download a load of apps. I wish (analogy coming) I could manage everything like a npm project, where I can keep all the dependencies under a single dir. I want to use my package manager to handle the dependencies, rather than manually downloading the bins, mv-ing them to the dir, and setting the path. Once I’ve finished building, dispose everything with just one or two commands, leaving no footprint on my OS/machine.

It’s better in one way, in that updates are applied on reboot rather than pulling the rug put from under running applications. But I agree that it doesn’t go all the way, as it doesn’t provide a verifiable base system with clearly separated modifications. OSTree would be great.

Another possibility would be to distribute a base image as a btrfs send stream (possibly differential against previous versions) containing a compose-fs image and associated files. And then OS extensions could be installed with systemd-sysext.