Let's take a break from breaking down the changes in various specs to talk about some changes coming to Death Knights. DKs have always had what might be the most complex resource system of all classes, with three different types or Runes, plus a special "Wild Card" type of Rune created by certain abilities or as a spec feature, and each pair of Runes functioning with odd cooldown mechanics and Runic Power on top of that, with talents that cause your Runic Power generators to refresh your Runes at a faster rate.
Things are getting a bit simpler in Legion, though I'd still say it might retain its title of most complex resource system - it just has more competition now.
As it looks right now (and remember, it's Alpha,) all Death Knights will simply have a set of six Runes. Not Blood, Frost, Unholy, or Death Runes, but simply Runes.
Ok, in a sense they're all Death Runes, in that they can be used for any ability that costs Runes. But they're just called Runes now.
The art is currently a kind of icy-blue skull, which some Blood or Unholy DKs might dislike as Frost favoritism, but I'm sure there will be plenty of addons to customize their appearance.
Runes still, I believe, regenerate at a baseline 10 seconds, sped up by Haste. However, without Rune types, you'll simply be able to regenerate three Runes at a time - they don't appear to be paired up the way they used to be.
Spending a Rune still generates 10 Runic Power (though some abilities generate bonus RP.) Runic Power spenders are also tied to two of the three "Rune Regen" talents.
The level 58 talent tier is all about Rune Regeneration, and Runic Corruption and Runic Empowerment are still there. However, Blood Tap has been replaced with Runic Longevity, which grants one extra Rune (for a total of seven) and increases your Rune Regeneration by 10%. I don't know how this seventh rune will play with regeneration - whether this means you'll be able to regenerate four runes at a time, or still just three. I'd suspect the latter, as that would put this more in line with talents and glyphs that would increase your max Rage or Energy.
Rather than a flat percentage, Runic Power and Runic Corruption appear to have a chance to proc based on the amount of Runic Power spent, though given that each spec really has one ability they're going to be spending RP on, it should look close to a flat chance, at least until you consider talents like Breath of Sindragosa.
The nature of Runes is a game-changer for Runic Empowerment, which I think will be a lot more powerful now. Currently, Runic Empowerment (and Blood Tap, though that's going away) is best used if you can game it. For example, in DW Frost you can try to always keep one Unholy Rune unused so that the one that you are using is always at least partially regenerating, so that Empowerment will be force to regenerate a far more useful Frost or Death Rune.
But with all Runes being equal, you're always going to be happy to get any Rune back, meaning that you can just spend every Rune you have and enjoy the return of Empowerment. It should also be pretty easy to use Runes quickly, as no matter what kind of Runes you have, as long as you have enough (usually just one or two) you'll be able to use the ability you're trying to pull off.
Combining this with the fact that each spec only uses one disease, and a lot of the more fiddly mechanics for Death Knights are getting smoothed out. I'll let you decide if that's a good thing or a bad thing.