WoWDB

Edit: Apparently this is meant to be a baseline buff regardless of quest status or server location. It does stack with Valor of the Ancients and also affects  Deeds of Valor.

UPDATE: This will not be going live with Patch 5.4.8 tomorrow.[1] However, more information will be made available at a later time."[2]

Considering how Patch 5.4.8 is primarily concerned with speeding up the MoP legendary quest chain, and that we already have  Valor of the Ancients, it would not surprise me if this buff is intended for those who are on A Test of Valor (A) / A Test of Valor (H).

Not that it'll make much of difference if a person has no problem reaching the weekly valor cap, however.

UPDATE: Has returned today, July 4th. There has been no word from Blizzard yet as to why this is, or how long it will last.

I'm unable to edit my original comment, so here's the following update:

...It's a temporary buff in the style of those used for Diablo III. I think Kaustos of US - Frostmane put it best (and the comment score agrees)

 Kaustos »

Increase Valor CAP by 100% and you'll have my interest.