[Disclaimer: I think the test server is testing out lockdown stuff if I'm not mistaken (friend told me about it). I have not been on the test server nor read anything about what is being tested.]
I think there should be the option for a 4v4 or a 6v6 match. The reason why I think so is because everyone has preference on how they like to play. I for one like smaller teams and maps while I've talked to some other players who find it more enjoyable for bigger teams and larger maps.
4v4 matches will always take place on small maps (3 control points)
6v6 matches will always take place on large maps (5 control points)
I am aware there are 5v5 matches but It would just cause more separation between the two.
I think part of the reason for having no option currently is because there are times when people leave during/after matches, making it more convenient to change between 3 and 5 points than to leave people waiting around. That is, if there are two 6v6 matches going on and each match loses 4 players by the end, it's more convenient to make them into 4v4 matches instead of one 6v6 match with four people waiting.
That being said, since there are people who are willing to wait specifically for a 4v4 or 6v6 game, there's no harm done in simply having the option. Since I personally have no preference, I would like to have the option to use the current system as well.