This.
I keep reading everywhere that it will be included soon, but I haven't seen any sources of 343 saying this (I haven't looked, either, because when I use Google, I find plenty of outrage threads instead of anything useful), just word of mouth.
I know this thread is about classic team slayer, but I'm going to divert a little bit. What I don't get is, you'd think it would make more sense to have SWAT as a stand-alone mainstay mode in multiplayer from the very beginning, you know? When I saw "Oddball" and "King of the Hill" with stand-alone mainstay modes, I was irked given the initial exclusion of SWAT. One would likely think it would be the other way around, with SWAT already being a stand-alone mainstay multiplayer mode from the very beginning of Halo 4 with "Oddball" and "King of the Hill" being added later, but no. Hopefully it's added within a couple of days (wishful thinking?). I like slayer, but I've only played 14-15 games of it and I'm already tired of it. I can't wait to get some one-shot headshots going on. That was the bread and butter for me when it came to Reach.
It's all good, though. I'm a decently patient person when it comes to getting a confirmation that there will be the inclusion soon. Hopefully soon!
The bottom line is, the game's been out for a day. Taking the emotions out and thinking objectively, we all know things will get patched up soon. Can't wait.