Blue post here: http://us.battle.net/wow/en/forum/topic/6308782635
This will implement the new talent & specialization system, the new glyph system and new glyphs, and the new "I no longer have to buy new spells from the trainer when I'm levelling alts" system. It may or may not implement account-wide companion pets and mounts, scenarios, and the new pokémon system.
I'm pretty stoked. :D
And for those of you who will be continuing your adventures into the Mists of Pandaria, I have one crucial piece of advice:
Empty your bags!
You are going to need tons of bag space. If you can afford it, get the biggest bags possible. Throw out stuff you keep kidding yourself you'll use later but then never do. Make a bank alt and shove stuff their way. Have a clearance sale.
The amount of things you'll end up carrying around during your stint in Pandaria is staggering, particularly if you decide to raise your cooking level and/or tend to your own farm (well worth it, considering you don't just farm herbs/vegetables but also plants that grant other items). You'll want to hang onto every cooking ingredient you pick up in your travels (raw ingredients drop infrequently from mobs), and there are somewhere in the neighborhood of 20 different types of foodstuffs you'll be carrying around at various points (or dumping into your bank at every opportunity).
As much as I'm loving testing this expansion, this is the one thing that's been frustrating for me throughout. I'm constantly having to destroy/pass up non-quest drops for lack of space!
Packrats beware!
Hoarders: Buried Alive in Azeroth. :o