afaik Plan9 already solved this issue - you had 'layers' of filesystems, not unlike Docker images/OverlayFS, with each process getting its own view of the files

afaik Plan9 already solved this issue - you had 'layers' of filesystems, not unlike Docker images/OverlayFS, with each process getting its own view of the filesystem. The last layer was non-persistent scratch. Of course you'd still need to reconcile writes to things like config files, which would be used by multiple processes, but the general approach is sound imo.