Hey Dualninja, thanks for your suggestion.
At this time we've decided to deny your suggestion and I'll briefly explain why.
Other team sizes are regularly suggested to us and massively supported by the community, however due to splits in our community these gamemodes do not currently pull enough players in those splits to function with these modes.
For example, we need to make sure that all games across all team sizes, input devices & regions are playable within a reasonable amount of time at all times of the day, adding most of these would disrupt this as at off-peak in the NA region on mouse/keyboard devices; games would no longer start for a few minutes depending on the mode.
It's our duty to make sure every player can join any game and start playing within a reasonable amount of time so that their experience is always positive, no matter what time they decide to play. In order for us to implement these team sizes we need to increase our player count substantially, then we can come back to this suggestion and see what we want can do.
The only one of this list that is possible at this time is Lucky Islands Duos, so I can tell you to expect that in the future. However due to the rest not being possible I am going to mark the thread overall as denied.