While that trinket is going to be on the 'BiS' lists of almost every tank, I wouldn't be too optimistic about the proc uptime. Due to the 60% trigger rate and the fact that avoidance will likely not trigger it (we will find out soon, I guess!) the average stack size is actually quite on the lower side of things.
For the average boss in ICC, I have been seeing the probabilistic uptime math on this returning in the range of 3-4 stacks, on average. However, this will vary heavily based on your avoidance rate and the swing speed of the boss. With the current duration and chances to proc, it is actually very easy for the buff to fall off unless it procs from avoided attacks as well.
It is still probably one of the best trinkets out there for both EH and survival time, however it only slightly beats the static 228 trinkets in terms of raw EH.
Personally, I intend on using Heroic Satrina's + Unidentifiable Organ until the heroic trinkets as I feel that use effect on Satrina's is much stronger than that of the ICC Stamina trinkets.
(I would also personally never gem Agility for a Warrior, although Agility would be a very nice splash stat to have on gear if Blizzard gave it to us. It's not worth thinking in terms of EH for matching reds--you match reds primarily, even in the case of Agility, to gain avoidance/survival time. 10 Dodge Rating is generaly about 30-40% more effective than 10 Agility in terms of extending survival time, which is the main purpose of avoidance gemmings. If you want EH, just toss in the Solid, the Armor from Agility is just too minor to make a big difference.
For Paladins, however, things aren't quite so clear. 10 Agility actually provides a slightly higher survival/burst time than 10 Dodge Rating, in addition to the slight amounts of EH bias. Thus, I would actually be fairly inclined to use Agility/Stamina gems in applicable sockets for Paladins.)