That seems cool, but I hope you don't end up in the place where namespaces ended up where there are too many security-sensitive codepaths in the kernel before you hit the sandbox. :) Unprivileged user namespaces exist but are disabled by default on many distros. It would be a shame for pledge to stay in the use case of "hardening programs that were previously running as root and that was okay" and not in the use case of "sandboxing actually untrusted programs".