I don't really see the benefit from this suggestion.
first of all what omma says, it'll have rooms where only one player is afk in the gamelobby.
next if u have an active room where players would want to join the afk player only takes up the spot for someone who actually does want to play.

Imo the way it currently is is fine. AFKs shouldnt be afk in an active room. being afk in the lobby is just fine.