I haven't played them in matchmaking yet. But with my experience with DLC is they always do a small section of just the new maps for now. Core mosh pit or something for a few months tell the next DLC than they will put into the usual line up with matchmaking. They can't do it yet because not everyone has them. So if they did put them up in matchmaking they wouldn't load properly. This is why they of only do a core mosh pit with the new maps.