Just me or does this read like the proposed solution to move the security boundary from cluster to namespace is to have a cluster per namespace?

Yeah, I don't quite understand it either as it'd be pretty similar to have one process per PID ns at the operating system level.

If you get blocked from the Google doc proposal, strip off the /edit at the end.

i.e. https://docs.google.com/document/d/1fj3yzmeU2eU8ZNBCUJG97dk_...