I don't really think Blizzard's intention is to fully compensate the mitigation lost.
To some extend they will, but we shouldn't expect our armor to be as high as it could have been with all those
armor pieces equipped pre-nerf.

This line direct from GC's post says that they will - or at least it is the current plan.

This is why I think it will be Str-->Armor and not AP-->Armor. Though how many +str buffs are in the game other than +stats and +stats%? The former we provide to ourselves the later would be a bit of a hit in 5-man content. Though we could make up for it with a scroll, food and/or a potion.

Honestly I hope they just 'keep it simple stupid'. Restore the base bear modifier to 400% (or even bump it a bit) and then have a talent that significantly increases the bonus bear armor. Change Thick Hide to something like 33%/66%/100%. Then either swap Thick Hide positionally with Natural Reaction or drop Thick Hide completely and bake it into some other deep feral talent like Natural Reaction, or King of the Jungle (admittedly im daydreaming on the last point )

Won't happen. It'll leave every druid using tier pieces only and nothing else.
They've stated explicitely (though I'll be damned if I can remember where) that tier items won't have additional armour.

My overall thoughts on this:

Overall it's a good idea. Picking the highest armor ring/trinket for any slot, regardless of other stats was stupid, and made us hang onto blue trinkets over epics.

On the other hand, they need to make some change to compensate. This means that feral tanks have only 2 mitigation stats for rings, trinkets, necks, etc: stamina and agility. Once you get "enough" stamina, it becomes only about agility. Basically it means that after a certain point, there's no difference between our tank gear and our dps gear. Which truly makes us too overpowered.

If they really want cat-druids to do roughly the same DPS as rogues, mages, warlocks, hunters, warriors, etc. it means a druid can be top 5 on the damage charts when the tank goes down. The hunters FD, the warlocks shatter, the mages inviz, the rogues vanish, and soon the feral druid has threat. Swap to bear form and the druid is tanking as well as the warrior, wearing essentially the same gear he'd be wearing while tanking... no chance of taking a crit, the same armor as he'd have in tanking gear, just probably a bit higher threat and avoidance, and a bit less stamina.

Honestly, I think they need all tanks to care about defense. Make SotF give us a 4% reduction in crits, not 6% and have us make up the rest in defense gear, but at the same time, make it so that defense gives more dodge if your class can't block or parry, and more parry if your class can't block. That way defense is a pretty good stat for druid tanks, and no tank can wear the exact same gear to do super high raid DPS as they do when they're the main tank.

You made at least 3 mistakes.
1) * 1.5 is only a 50% increase, for 150% increase you need 2.5
2) You added the weapon armor, which was stated quite clearly as removed
3) Poorly thought out wish lists don't belong here

The actual armor from your method would be: 48910.5

I also am looking forward to not being shackled to one specific trinket/ring with armour. As for compensation, it's been mentioned to have AP/Str with some modifier being converted to an armour value. Seeing as one of our problems is too few stats to focus on, why not give us an armour value based on ALL our stats? Add it to a deep feral talent like Heart of the Wild if there's concerns re: restos and arena.

Granted, we'd still run into the situation were buffs make a significant difference, but without a modifier, you'd not notice a large change in mitigation if you lose a single stat buff during a fight. It'd also have the side effect of sparking some further interest in a broader range of item drops.

We won't get parry. At least I would kind of hope we didn't. That's a very boring solution to our problems right now. Give us parry and we're a Death Knight with different threat building attacks. I never understood the fact that mobs that aren't wielding some sort of weapon could parry anyways (and being in form should negate that we carry a weapon as it isn't visible).

I do agree with some of the points that Str or AP -> Armor would be an awkward fix though. But we already get some armor from Agi and allowing it to do more would be too much from one attribute, so something like AP -> Armor makes at least some sense as we are tanking in DPS gear with tank gems/enchants.

Baking in another armor modifier into PotP or even KoJ won't happen either unless it is at the expense of something else as then those talent points become to over budget. If it goes into PotP it would need to replace the AP modifier, but would still be over budget as that is more of an addon to the % damage reduction. If added to KoJ it would need to replace the % damage increase, but that would make it just another mandatory talent to take which we already have a fair number of.

We made it through BC on green armor. That screws up item budget so I'm glad that won't be coming back. We need some sort of PvE stat that will increase our mitigation so we are not relying on PvP items for PvE.

This actually fixed the PvP gear problem, because just as cloaks, the way our armor will be calculated is (ilevel armor value * Bear_Modifier)+extra bonus armor, meaning that the large armor gain from PvP gear will be gone and that pretty much removes the desire to use the PvP gear for PvE. Regarding strength -> Armor instead of AP -> Armor, keep in mind we barely get strength on our gear, our tiered gear has no strength, the rogue leather doesn't, the only pieces with strength are tanking jewelry.

I can't remember which forum I read this one, but someone suggested that armor gained from agility should be affected by the bear modifier. This would help us bare taking the dps gear we are being forced to take. The only problem I saw with this suggestion was that we are pretty much replacing bonus armor with agility. We would start drooling over agility rather than armor.