Mage gameplay has kind of been a gold standard through Warlords as far as fun-to-play has been. As such, the Mage specs are not really changing all that much. Rather than tearing things down and building them up anew, each spec is really just getting some tweaks. They've all been pretty solid on the class fantasy and spec fantasy fronts (Mages magic at things until they die. Sounds about right!)
As such, this is going to be far less shocking than, say, the Survival or Demonology changes.
But I'm on a roll here, so let's get this one out there! As usual, take things with a grain of salt, since this is based on an Alpha build. That said, given that most of this is just a tweak to the existing design, I wouldn't expect anything super radical.
Frost is going to probably miss Multistrike more than other specs, given how easy it is to get instant spells that almost always crit (essentially giving you a low soft crit cap.) Also gone from the rotation is Frostfire Bolt, which I personally think is a travesty. Blizzard justified this removal by asking how a bolt of Frostfire would even work. Shouldn't the fire melt the frost? My answer? It's MAGIC! BECAUSE WE'RE MAGES! Seriously, Frostfire Bolt is one of the most gorgeous spells in the game, and I loved that Frost got to retain a little bit of out-of-element bleeding.
Ok, I've calmed down. At least on WoWHead, there seems to be some old information, like references to the lost beloved Frostfire Bolt, so there might be some out-of-date info here.
Frostbolt remains the heart of the rotation, taking 2 seconds to cast and dealing Frost damage while slowing the target by 30% for 15 seconds.
Ice Lance is an instant-cast spell that deals Frost damage to a target, and does double damage when the target is frozen (or if it "counts as frozen" thanks to Fingers of Frost.)
Frostbolt and Frozen Orb (Frostfire Bolt is still listed as well) have a 15% chance, and Blizzard has a 5% chance to give you Fingers of Frost, which allows you next Ice Lance or Deep Freeze to treat your target as if it is frozen. If you use Ice Lance with this, it will increase its damage by 140%, for a total of 380% of normal damage. You can have two stacks of this buff.
Shatter is a passive that increases your crit chance against frozen targets, multiplying it by 1.5 and adding 50% (so, against a same-level target, this effectively gives you a critical strike soft cap of 33.33%)
Frozen Orb has a 1-minute cooldown, sending an Orb of frost that lasts 10 seconds shooting forward (slowing down when it reaches a target) and that damages all enemies in its path and slows them by 30% for 15 seconds. The first time an orb deals damage, it automatically grants a charge of Fingers of Frost.
Brain Freeze is a proc that gives your Frostbolts a 10% chance to reset the cooldown on Frozen Orb.
Blizzard now has an 8-second cooldown, with a 2-second cast time. It deals Frost damage to a targeted area over time (I'd assume 8 seconds, but don't hold me to that.) Each time it deals damage, it reduces the remaining cooldown on Frozen Orb by 0.5 seconds.
Cone of Cold is an instant-cast spell on a 12-second cooldown, dealing light Frost damage to everyone in a cone in front of the caster and slowing them by 30% for 15 seconds.
Icy Veins is a 3-minute cooldown granting 30% haste and preventing all spell pushback for 20 seconds.
Summon Water Elemental summons your permanent Water Elemental pet. We don't have a list of abilities, but I'd assume that it's got what it has now - though we don't know the fate of Water Jet (personally I like it - giving you an option to deal with Fingers of Frost dry spells when you can't use Freeze.) There is a talent option that allows you to go pet-less, which makes Freeze one of your spells, so I'm confident that will be on the pet's bars.
Mastery: Icicles remains much the same, granting you an Icicle when you cast Frostbolt that is proportional to its damage that lasts 15 seconds. You can store up to 5 at once, and if you get a sixth, the oldest Icicle will launch at your target, or if you cast Ice Lance, all 5 will launch at your target in quick succession. (This portion of the Mastery really just effectively buffs the damage of Frostbolt.) It also increases the damage done by your Water Elemental.
Overall, the rotation looks mostly the same, but you'll be casting Frozen Orb considerably more. Given that it's only on a 1-minute cooldown, you're probably already casting it whenever it's up, but now you'll certainly want to do that all the time thanks to the new Brain Freeze. So before we get to artifact traits and talents, here's what we've got:
1. Ice Lance if Fingers of Frost is up.
2. Frozen Orb on cooldown (keep an eye out for Brain Freeze.)
3. Freeze if you can hit a target that is not immune to it - preferably two or more.
Once you get I want to say 5 targets or more, you want to start using Blizzard to get your Frozen Orb off cooldown instead of Frostbolt. Though if you can maintain Blizzard and squeeze in some Frostbolts, go for it, as you might be able to just reset Frozen Orb. With the changes to glyphs, the fate of Glyph of Splitting Ice remains a mystery. This is one of the few glyphs I've always thought is a 100% mandatory one, unless you're on a strictly single-target fight (and how many of those do we see these days?) Talents like Ice Nova and Comet Storm seem to be remaining, so you'll have other buttons in your actual rotation if you want.