I'm not sure why I haven't been reading the blog, but I just added it to my regular reading list...
I read through those latest articles and another possible match making encouragement method sprung to mind.
I think many people are in favor of an ELO system (for all the faults of ELO systems) for competitive match making. That helps established players, but not the newbie drop off rate discussed.
You'll have the filters you talked about which seem like a short cut way to draw a line between standard and "ranked" matches.
What if you added a game quality bar of some kind. Kind of like how in many online games you can see the latency of a given match to determine connection quality.
Newbies show better "connection" if the match meets certain criteria, and more experienced players the same other criteria. Too many new players in a match would probably be less favorable to add more new players. Medium or low ranked experienced players might be a better environment for new players.
The idea would be to have two specific goals and then let everything else just fall into place.
Goal 1: Show favorable game conditions for newbie games to decrease drop out rate
Goal 2: Show favorable game conditions for experienced players of similar ELO rating (bonus on this would be a player could tweak a "difficulty" so they could alter the favorable conditions.)
retroactively apply this system to past games and examining those games drop out rate should allow you to tweak the game rating algorithm prior to implementation to get it just right.
This might all be too much to implement, or it could be unnecessary.
I have no idea which, but unless you grow this slowly (through metered invites) until the communities can't be hurt by a large influx of people, it may be hard to overcome this issue.