My point though was that at the implementational level, the old symlink-based way of implementing it in Nix is severely lacking the isolation and more general security capabilities of the bind-mount, namespaces and cgroup-based approach of OCI and other newer packaging systems. And Nix needs to implement that.

My impression is that the OCI package spec isn't what would be in the way of implementing a system that would combine the isolation and security of a system based on bind-mount, namespaces and cgroups like OCI with a graph topology like Nix and that there would thus be an opportunity to combine the two, which would help Nix take over the dominating position in that space. If OCI turned out to be impossible to use with the more graph-based approach of Nix, then that would mean a much higher implementational work - not that it couldn't be done, but it still would need to be done then. But either way, Nix cannot stay with its old symlink-based layering: Failing to implement the security features that are now expected from modern packaging systems (isolation, bind mounts, cgroups, namespaces etc) is a surefire way to progressively maneuver into irrelevance.

Nix has a window of opportunity here due to the current weakness of the big players in the field. But it can't afford to let that slip.