From the live letter.

We will be changing the method for calculating the potency of physical attacks for tank roles in Patch 3.2. We’ll be making it so vitality affects the potency of physical attacks, and as a result the effect of strength on physical attack potency will be reduced.

From Patch 3.2 onwards, you’ll be safe using only vitality accessories as well as allocating everything to vitality as a tank. For everyone who is currently using strength accessories on their tanks, the damage will be lowered, so please prepare your vitality accessories ahead of time.
Looks like full str tanking is dead come 3.2. This must make healers happy.