Arguably, Frost Death Knights are getting the fewest changes of the three DK specs, despite the fact that many of us long-time 2H Frost folks are being forced to dual-wield.
Looking at the abilities as they've been laid out, it actually looks like the 2H rotation is actually the one that the spec will be more similar to, now that Killing Machine only affects Obliterate. This should hopefully keep the ability relevant and at the heart of the rotation. On one hand, I'd like to see Obliterate get a talent that either modifies or replaces it, making a powerful frost-attack, but on the other, that would mean that everything Frost did was, well, Frost, which is a little odd for a melee spec.
That's always been the problem with Obliterate, since Mastery was introduced in Cataclysm. It hits very hard, but it doesn't scale with one of our core secondary stats. Mastery is, of course, meant to scale differently between different abilities so that it's not just a "you do X% more damage," but the way it's worked out for Frost is that the strike that should arguably be the keystone of the rotation is the one thing that really doesn't benefit from the stat.
In Mists and Warlords (I believe in Cataclysm the emphases were flipped, with DW favoring Obliterate over Frost Strike) this meant that 2H Frost DKs would actually keep Mastery on a low priority, preferring Haste and Crit in Mists, or Multistrike in Warlords.
The rotation was somewhat simple, but required quick judgment calls on whether to blow your runes when KM was not on, risking not having them up for the proc, or burning RP for Frost Strike, hoping you don't waste a KM proc that popped up right as you hit the button. If you were really good, you could work out your swing-timer to try to make sure you played ideally.
Ultimately, that rotation had a priority of Diseases, Howling Blast w/Rime, Obliterate w/KM, Frost Strike, Obliterate (it was more nuanced than that, but that's the basic gist.)
Theoretically, dual-wield should have been the inverse. With Frost Strike buffed more than Obliterate when dual-wielding, it should have been Diseases, Howling Blast w/Rime, Frost Strike w/KM, Obliterate - and maybe if you couldn't Obliterate, you'd burn a Frost Strike for rune-regen.
In practice, however, the Masterfrost build started getting traction, where you'd simply load up on as much Mastery as possible and spend your runes spamming Howling Blast instead of worrying about Obliterate. You'd spend you Unholy runes on Death and Decay (single target as well as aoe) and "free" Plague Strikes to keep up Blood Plague. Obliterate got a little play in Warlords thanks to a buffed Rime proc (though it wasn't called Rime anymore) but it was/is definitely low on the priority list. Unlike Frost Strike, which is always going to be how you spend your Runic Power, Obliterate got overshadowed by Howling Blast.
HB is a really cool ability, but it didn't see to be working as intended, which is why I think they're pushing for this version of Frost.
The key, I think, for their design is that they've got to make sure that Mastery never gets so high that Obliterate can be dropped from the rotation. I think a more exciting thing to do would to be to make Obliterate do more interesting things - it already has the Rime proc, which is good, but at the moment, between Killing Machine and the fact that it's physical damage, Obliterate actually manages to de-value two of the four remaining secondary stats. Giving Obliterate new ways to scale - either by changing KM from an auto-crit to a double-damage proc (realizing of course that a KM Obliterate crit might be too large) or adding new features, either through passives or talents, that makes Obliterate really awesome, would be a good way to keep the spec working as intended.
Frost DKs already had pretty flexible runes, with the Blood runes automatically transformed into Death runes, and with the loss of Blood Plague and Death and Decay (see below,) I actually don't think that the Rune change is going to hit them all that hard. It does mean less awkwardness around the Runes, which admittedly will simplify the spec (well, class,) but rune-juggling isn't terribly hard for Frost already, and it shouldn't totally trivialize the spec.
I also like that Frost is getting Remorseless Winter as an AoE damage ability to replace Death and Decay. Certainly, DnD is one of the most iconic DK abilities, up there with Death Grip, but it always felt the least appropriate for Frost, given how shadow-based it was. I imagine RW will be weaker, given that Frost already has Howling Blast, but it remains to be seen.