Currently there are a lot of suggestions for new matchmaker queues. But I'm afraid the player base is way too small for having that many queues running at the same time. Also maintaining that many pools is quite a lot of work. Instead I would propose having only one additional queue which has a different theme every pool rotation. For instance only mapgen team games, only 5x5 1v1s, setons, phamton, SCTA, shared armies, survival and what ever else might be fun.
It would also give the matchmaker team the opportunity to test out certain maps/concepts that are too experimental for the competitive queues.
In other games these special events/ minigames are very popular amoung beginners/ casual players.
For putting it into practice: I expect that launching 3v3+ matchmaker games is only a matter of time. I suppose having mapgen maps in the matchmaker is also planned. How hard would it be to add mod support?
Maintaining the pool would be a lot more work than the usual 1v1/2v2 pool. As every month you would need a new concept that is somewhat coherent. I could imagine some modders/ mappers being motivated enough to propose a whole concept (which would highlight their work) which would only need some adjustment. At the end of the rotation it would be very important to evaluate how well the current concept was received. There will be a lot of bad ones for sure.