First off, a big old grain of salt: When Mists of Pandaria was in beta, the way that Brewmasters worked was very different. Shuffle was not a buff generated by Blackout Kick, but a channeled ability you were expected to use, eschewing all damage abilities in favor of survival. So these things can change.
But for now, here's what we've got:
Vengeance's Mastery seems to be based on what could be one of the spec's major themes - namely Parrying. This makes a lot of flavor sense - Demon Hunters generally being characterized as a flurry of Fel-powered blades. The Mastery, Glaive Master, increases Parry chance. For now, it looks like it will be pretty much flat-out Parry Rating (though I'd assume it will also have the standard attack power buff that comes with all tank masteries these days.)
There are other passive relating to your parry chance, including a flat damage reduction in Blade Turning and what looks like a primary Active Mitigation ability, Blade Barrier, which increases your parry chance by 30%.
Vengeance has some good mobility - in addition to the existing Demon Hunter abilities like Fel Rush, there's also Infernal Strike, which looks like a kind of Heroic Leap-style ability that might be on a shorter cooldown and has multiple charges.
Additionally, they have a number of "Sigil" abilities, that allow them to put ground-targeted sigils which go off after three seconds, doing things like silencing, taunting, or pulling the targets to the center.
Shattered Souls is an ability both specs get, and while for Havoc it's probably more of a soloing ability - much like Monks' Afterlife, it creates a little object on the ground that will heal you when you run over it, generating it after you kill a target. Vegeance, however, seems to be able to generate these Soul Fragments more often, giving them some self-healing - a bit like Gift of the Ox, though it looks like DHs will have a way to pop those fragments without running over them in Soul Cleave, which is a melee strike that also consumes these fragments. While in Metamorphosis, which baseline increases max health and reduces incoming damage both by 30%, your Hateful Strike (which looks like a primary Fury-generator) is guaranteed to spawn one.
One of the fun little flavor things for Shattered Souls is that if the Soul Fragment came from a demon, you get a little damage buff on top of it.
So the image we're getting is of an avoidance (but not dodge!) heavy tank that also has some health buffs and self-healing. (Actually, with Monks and Druids both moving away from avoidance as their main source of damage reduction, there's an opening for Demon Hunters there.)
Big caveat though: nowhere in these datamined abilities is there any mention of the Pain resource. It's possible that Pain is on the cutting-room floor, but it's possible that these abilities are from an earlier build, or that we simply don't have the full picture. Given that Demon Hunters' voice emotes make mention of Pain (there are error messages for "Not enough Pain," etc.) it would seem that at least at some point, Blizzard was very confident about using the resource for the class (though to be fair, there are also error messages for mana, energy, rage, and even focus, I believe.)
Still, as someone who will probably try to go tank-spec on my Demon Hunter, I'm eager to get the details on how they'll work.