I literally chuckled when I saw your message because I actually thought about using dom/sub when I saw the '"dominatrix"-"submissive"' message, and there's the bonus of it being more symmetrical and less typing than master/slave.

The deal killers being that it's less readable due to the lack of established usage and that it doesn't define the relationship as clearly as master/slave. It feels like "dominant" might imply that it has authority in most cases, but not every case.