How about a pin for MCP to prevent users from hijacking a moderator's account and abusing it? And a forum board password so when the board is down, certain people with the password can access it.
If an user can hijack another user account, he can potentially hijack ad admin account rather than a moderator one and do several more damage. IMHO, it'd be a pointless feature.
If your board is down, you cannot access it either so setting up a password is pointless too.