PVP

Useful PVP information:

• WOD Arena Season 16 Sets Preview

World PvP
A new World PvP zone, Ashran, will be level 100 with constant fighting--think the Timeless Isle, but PvP.
Ashran is a staging area near the Dark Portal that the Horde and Alliance want to control. It has a variety of hotspots to control and faction hubs.
Different than Wintergrasp in that there's no start or finish. It will not feel like an instanced battleground.
Objectives will rapidly change based on the zone's events--you could go from attacking a base to gathering defensive materials quickly. Ashran will feel like original Alterac Valley.
There is no limit to the amount of players allowed in the zone and this zone will be cross-realm.

Arena
Skirmishes will return as a form of unranked Arena play that will allow players to queue for 2v2 or 3v3 battles with friends or by yourself. Winning a Skirmish will reward you with Honor and a random bonus--such as gold, more Honor, a small amount of Conquest Points, or possibly something entirely different.
The new Spectator Invite system will allow a match organizer to invite two teams to play against each other in a PvP spectacle called a War Game. Everyone in the party can watch these teams play.
A new arena system announced at BlizzCon, Trial of the Gladiator, was later announced to be scrapped in February.

Battleground
Battlegrounds are getting some improvements to be more appealing.
Battleground score is a new stat that tracks and rewards players for objective-based gameplay. With Honor Points, it might not feel rewarding to stay back and guard a base, but with Battleground Score, you'll feel more compensated and get a better sense of how well you're doing.
Objective timers will be viewable on the map, and they will have additional animations.
Battlegrounds are getting additional bonus rewards as incentives to win, such as PvP gear, bonus Honor, consumables, BoE items, and more. Honor point rewards are also staying in place.
New weekly quest to upgrade an item. Not sure how this will work, since item upgrades were disabled for PvP items in MoP.