I get the impression that a lot of the time when more selective MM is mentioned it is soon followed by talk of increased queue times. So I want to leave you with this to think about.
From my experience getting a game when there are 3k+ players on the server is no problem. At peak there are 3-4 times that number. Point being even if MM removed half the players from your MM pool (so that MM was more appropriate) there would still be, by my reasoning, plenty of players and short queue times.
That's all.