You could, but I have not included it for various reasons. I apologize for omitting my reasoning for its exclusion. I pushed myself to complete this thread the day the proposed changes were posted, whereas my last thread was a week in the making (which is why it was such a wall of text).
Stoneskin is in a rather awkward place with respect to eHP. The 3-second cast means that when an enemy is using autoattacks, you can't really rely on it due to the possibility of interruption. That makes it somewhat inappropriate for inclusion as eHP (just as blocking, evasion, and so on are not included). It could theoretically be applied with some degree of certainty if you drop Awareness, but that currently makes heal crits on you impossible. Additionally, the window in which it must be dropped is extremely narrow (no more than 3 seconds due to being cleared by an autoattack unrelated to the burst), it is incompatible with a healer's own efforts, and you need a window of 5.5 seconds between last GCD and completion of cast to get the cast off. Finally, it also is not a unique effect to one tank -- a PLD or WHM can cast it on a WAR just as well. For these reasons, I did not include Stoneskin previously and still have not included it.
I did not include Featherfoot, and I do not have any data on the stacking of blind and evasion effects.
