This is a custom feature. And, if we're moving a little away from being most blizzlike as possible, there's a lot to consider such as where the chest will spawn. Spawning it close to a horde capital, that you can get there through portals or a hearthstone, makes it way easier for the horde players and alliance players will not be encouraged to play this.
While it's a nice little thing, I think it's not needed to encourage world PvP. Take a look at Neltharion and Frostwolf, both realms have an active pvp community already.
Perhaps it can work for PvP-only realms, but not the others. I rather keep a full blizzlike experience.