Team Swat and Team Snipers are a whole different animal than regular team slayer, but I understand what you were going for. On average, how many players are in BTB at any given point? Team Slayer is roughly 8,000 on average. I know BTB is less than that. So, you put BTB Heavies in its own playlist. Now, everybody that wanted heavies moves over to that playlist, cutting down the number of players in regular BTB even further. It'll slow down matchmaking already. I played BTB the other night, waited for 5 minutes before I ever found a game. Team Slayer or Super Slayer? Average wait time is less than 30 seconds.
As for the DLC, I fully agree that they should do a BTB DLC, even though the maps are few and far between. I've only ever played on a few of the DLC big maps, and it's by pure luck. As for not purchasing Halo 4 DLC because it requires "luck" - - that's a fault of Reach. Look at Halo 3, nearly everybody had all the DLC and it was a great game that people loved to play. Reach broke that, and a good portion of the population didn't agree with the approaches that Bungie took. If Halo 4 turns out to be as good as H3 (and don't get me wrong, of all the Halo's so far, Reach is my favorite, love the game), more people will gravitate towards that, and thus more DLC purchases, making BTB DLC maps easier to come across.