I like the idea of allowing more players in round robins, but can see why there would be pause to do so. A pool of 10 players creates 45 games to be played out in the tournament. A pool of 16 would create 120 games. Quite a difference for 6 players.
I think it would be cool to enable some kind of progressive round Robin pool play where a tournament consisted of several round Robin pools. After the initial round everyone would be reassigned to a pool based on results aka champion'so pool, 2nd Tier, "loser's" pool...
Of course this could be done now using invitations by the tournament organizer with some work, but there isn't a way to prevent someone from registering in all of the initial pools...at least that I am aware of...