KevinIsPwnOnd_kajaQueue system for slots isn't a good idea because it slows down the start of lobbies since people would rather elect to queue for a scout spot rather than add up as medic or demo. TF2Pickup used to have a similar system and there were like 10+ people queuing for a scout spot or something ridiculous like that.This is not a final feature, but just an idea proposed by the devs a while ago (shown in the progression of the site).
To add to this, that image isn't even a screenshot but a mockup. There was literally 0 code behind the picture.