I love FoS as much as the next person but i do not think it will become a feat.
Feats for legendaries were usually given to specific set of classes that could use it.
However, this is not the case.
It would technically be a hand me down FoS for completing a easy chain in comparison to previous legendary chains and RNG factor.
Feats of Strength should be reserved for things that take actual effort, such as logging in during WoW's anniversary
Wutudidthar, icit. :P
I think that completing the entire chain, not just getting the cape, should become a FoS. That would include a Garrosh kill, which is the next part of the chain. You don't get credit for completing this chapter of the Wrathion story until then.
There is a guild-related achievement: Shroud of the Celestials-Guild Edition. No personal FoS, just the 25 point Chapter achievements you already got, another rep at Exalted, and the main reward of hearing Aaron Phillips' voice acting.
I could support a FoS for the cloak if they had not made the previous steps of the chain much shorter. It did take alot of effort to get it before they nerfed the VP quest and buffed droprates and places the sigils/stones/secrets could drop. Yes, even in LFR, it was a lot of work, more so than the rogue daggers IMO and much more time consuming.
Giving it a FoS now when you can get is so quickly wouldn't be fair, though I could see them making it a FoS for getting it before the next expansion like the Ahead of the Curve achievements.