I've always liked the word "Cossack." It's fun to say, it's got two c's and two s's, it's how John Cusack's name should be pronounced, and it's basically a mashup of "cock" and "ballsack."
So I was with the Cocksacks until the letter-writer in the trailer above starts going on about "Turkish devil" as I am behind the Turks 100%. They have a very cheap international airline and delicious kebab. Good god I am hungry now.
Anyways, The Cocksacks are coming to Europa Universalis IV in late 2015 as DLC, though in typical Paradox fashion, players who don't purchase the new content are still getting a major update for free, as detailed in the Paradox blog.
The biggest addition is the Estate system. "You can assign control of your provinces to local factions – priests, nobles, or even Cossacks! – sacrificing some income in the name of lower unrest, more manpower or cheaper cavalry. You must keep an eye these Estates, though! If they get too strong, they may make a move on your throne. If they feel neglected, they may interfere with efficient governance."