DJB's suggestion of how to isolate a process

The quoted text is in the context of what one can get with “existing UNIX tools”. The paper goes on to claim that short of “severe operating-system bugs”, the result is that the process “has no communication channels other than its initial file descriptors”.

Does anyone dispute this claim, or have a better suggestion of how to implement that result with standard UNIX interfaces?

(I haven't looked into the bug mentioned, though I'd guess that isolate(1) is a world-executable setuid utility that has a bug allowing arbitrary code execution before doing the setuid step, rather than being a bug in the approach quoted from the DJB paper. Anyone who's looked into it, please either confirm or refute this guess.)