I am suggesting this primarily for Extension:SecurePasswords (which is not listed as a component). However, it could conceivably be implemented in core (at least the length part), or another extension.
Allow setting different requirements for different user groups (admin/sysop, buearuacrat, steward, etc.). This allows making the requirements for users with elevated rights more stringent than for just editors.
This was discussed in the now-closed bug 16435.
T18435: New extension to enforce minimum password strength.
T27925: Increase $wgMinimalPasswordLength