Rewarding exploration is by far the best way to encourage world PvP, the two are tightly linked together. The reason world PvP was so prominent during Vanilla was because Azeroth was still relevant and people had a reason to venture outside of their cities to do things. Adding an incentive for people to roam Azeroth once again will result in more world PvP overall, at all times. Whereas adding an incentive to go to a set location or two, at a set time period will result in more "world" PvP in those set locations for a few hours before everyone hearths back to Dalaran to play bejeweled while they wait for their queues to pop up.
I suggest at least drastically increasing the number of zones these chests spawn in, splitting the reward into smaller pieces with more frequent spawn time and making them appear in hand-picked, attractive for PvP locations in Azeroth like Blackrock Mountain, caves, city ruins, places with multiple elevations and uncommon terrain.
This guy has the right idea. As much as vanilla players like to nostalgia all over their screens when it comes to Southshore vs Tarren Mill, the middle of Hillsbrad is as dull as it gets in terms of cool things you can pull off. The goal here is to create multiple smaller world PvP hot spots with potential-rich terrain that are constantly active as opposed to one big melee that is active for only a few hours a day, like some sort of malnourished twin of Wintergrasp.