Now: Most tanks have sufficient Effective Health going into raid content.
T8: You will not be able to get enough Effective Health going into T8.
Blues done right (enchants, gems), or half-done ten man / crafted / heroic gear puts most tanks (in most groups) at a comfortable level for Naxx & OS+0. More Effective Health is icing on the cake, and your healers certainly won't complain, but your already feel pretty safe.
In T8, we will find ourselves at the bottom end of the gear level that Uludar was tuned for. Damage that is suppose to be dangerous to partially/fully geared-in-t8 tanks, will be nearly lethal. To not get yourself one / two shot - you will need as much effective health as you can get your hands on.
Now: Given your safe amounts of EH, you are free to wear gear that is gemmed/enchanted for avoidance, threat, or even spellpower/spirit/looks.
T8: You will not have that luxury.
I could regem full avoidance, and do fine in T7. I could go full threat gear, and be perfectly healable (as I often do, including last night's Malygos, w/ 4 healers). Some people will go these routes, pull off some fancy stunts ( I did a hojillion TPS, became passive unhittable, or solo-tanked patchwerk for 50%) - but its just all a sideshow.
Tier 8 will require the responsible tank to trim "fun" stats, at least in their primary gearset. There are a great number of gear pieces that are a mixture of (only) dodge/parry/defense, and stamina/str. These are going to be so worn out and smelly by the time you drag your body to Yogg-Saron, you won't be able to pry them off your body to replace them.
I don't doubt that there will be fights that aren't as punishing as others, and fights that may push you to wear threat gear to keep up with hella buffed DPS - but these fights won't be ones that you need to be gearing around. Your gear, as a tank, is most critical on fights where bosses will try their damnedest, and may succeed, at killing you.
Now: You (should) have multiple sets of gear.
T8: You will have to work with the upgrades you get.
The "threat" statted helm you get in T8 first, may be a better EH helm then your current one. Do not hesitate in gemming / enchanting it for EH. Yes, there may be a better EH helm off another boss. Yes, when you get that one, you will want to completely regem this current helm to threat. Yes, that is expensive. But if your making stingy choices about how you spend your gold, your really making selfish decisions about how the raid's time is getting spent (wiping, versus progressing).
(Think about how much time a single wipe takes for 25 people, including the run back, rebuffing, ect. We'll say its a fast wipe and return, so 5 min. That's over two hours of people's time. There is no tank enchant/gem enchant that is going to take you more then two hours of time to grind / get the gold for. Saving even a single wipe from correct gear enchanting is worth every copper).
So crank your EHealth up to 11, and prepare to rock in the Halls of the Titans.
What game companies can learn from Albion Online
13 hours ago