Have a per member sandbox for certifications
We could imagine the sandbox of certifications to be per member.
Because as we know we have max sigWindow/sigDelay = 60 days / 5 days = 12 pending certifications issued per member, then cert_sandbox_room = 12
would give us an absolute room size just depending on N.
So any certification would pass for any member as long as he limits himself to 12 concurrent certs, and be refused from non-members of course.