Spirit Link

Spirit Link Rank 1
12% of base mana 40 yd range
Instant cast
You link the friendly target with up to two nearby friendly targets, causing 50% of any damage taken to be distributed to the linked targets. If any target takes a blow greater than 30% of their health, or shared damage would reduce a target's health below 20%, the link is broken. You can only have one link active at a time.

Is it just me or is this earth-moving? Instant cast, 30-second duration. If you have two willing damage soakers, this spell will halve incoming damage to the tank. From my point of view, that means the following for difficult raid boss tanking:

Either (A) Spirit link will become standard for all boss fights, and a raid requirement, or (B) Goodbye insta-gib.

Spirit Link fundamentally changes the way tanks will gear. If insta-gib is no longer an issue, then avoidance gearing will be 100% the way to go. EH is no longer a concern if Spirit Link is up, therefore the role of a tank would be to reduce as much of the incoming damage as possible to reduce the healing load, while producing threat. The new BoSanc provides the solution to dodge/parry rage/mana starvation from avoidance gearing.

Spirit Link also solves the rage/mana starvation issue that BoSanc doesn't. That of off-tanking in order to keep threat up when the OT is not taking enough incoming damage or attacks, e.g. Gruul. Spirit Link the Pally OT, heal the Pally up, and voila, mana back.

Blizzard has said that one of their goals in WotLK is to make tanking specs do more damage, and to make some dps specs able to tank, such as ret pally, and most DK specs. Spirit Link provides raid roles for such dps/tank hybrid specs. They have the stamina (and possibly mitigation) to take 25% of a non-SL'd tanks incoming damage, as well as raid damage, while still able to put out respectable dps.

If encounters are re-tuned so that in order for tanks to survive, Spirit Link is mandatory, option (A) above, then all requirements for spirit link soakers go up. Raids will bring mandatory spirit link soakers, specced and geared prot, or for multi-tank encounters, may have multiple hybrid classes capable of acting as soakers for the heavy damage tanks. This still synergizes with Blizzards stated goals about hybridizing a bit of the prot/dps roles. Paladins of course, also hybridize prot/healing roles.