@blackyps
The existence of a 3v3 map gen only queue does not preclude the existence of a 4v4 map gen only queue.
3v3's and 4v4's have some similarities, but each has benefits that the other lacks. A 3v3 is not the same as a 4v4; if they were, we wouldn't be having this discussion...
Personally, I think that we should have map gen only TMM options for every player count that we have TMM for. Regardless, we definitely should have the ability to play 3v3 TMM, and we definitely should have the ability to play map gen only TMM.
If the problem with implementing a 3v3 TMM is a lack of good 3v3 maps, then making a map gen only 3v3 TMM is a sensible way to kill two birds with one stone.
I would still hope that other TMM options/queues are added later, and adding a map gen only 3v3 TMM queue wouldn't prevent that.