My initial toughts on everything:
Agility now gives leather wearers 2 AP, but AP is gone...what happenes to AP items? To fully estimate an answer, you need to think of items like Mirror of Truth, Fury of the Five Flights, ect... The OVERWHELMING majority of trinkets at endgame give AP. Only DMC: Greatness gives straight strength. I dought they will completely bork all Strength users by just converting all AP to Agi. Perhaps they just leave AP gear as-is? Its obviously still a stat since Agi will give 2 AP. Maybe they just phase it out so there isn't any on level 85 gear.
Spell Power is gone. Intelligence now gives Spp. Something is going on with Ragnaros...who knows what MC will be like? Time to farm the rep for +22 int to weapon and farm the drop for +20 Spp and see how it plays out.
MP5 is gone. Will 19 healers have the meditation ability to convert spirit to in combat mana regen? I doubt it. If it was that low in the tree, DPSers would pick it up.
Hunter mana is gone. Hunters will no longer gear for intelligence. That means new incomming hunter talent in the Marks tree to replace Careful Aim. Possible DPS nerf with the AP loss...though they will just be able to gear for straight Agility now. Start looking for replacements for that falcon gear. Wope you didn't spend a fortune on the Wranglers. Get your Desolace ammo NOW, just in case. Desolace is getting revamped.
Southshore going to the horde, level 85 SFK/VC, Barrens torn asunder. What happens to all the quest rewards? Deadskull, Inferno Robe, Wingblade, etc...
New races mean new starter zones mean new quest rewards. Keep an eye out.
REFORGING:
It will be relatively cheap, you will need a Blacksmith / Leatherworker / Tailor / Jewelcrafter / Engineer to do it. Each profession get to reforge a type of items.
It lets you reduce one stat for another. Some restrictions will apply, you can't put the extra stat on something that is already on the item.
Wow...if useable on low level items, this could make gearing interesting. Spidersilk Drape with 4 stam/4 hit/4 crit? Honor Neck with 6 Int/2 Stam? ENGINEERING GOGGLES WITH 8 STAM/7 <ANYTHING BUT SPIRIT> KISS MY ASS KEEFER'S I AM NEVER FISHING AGAIN?
Lots to watch.