Right now we have PvP in our otherwise PvE Timeless Isle. There are also PvP quests to complete for the legendary cloak. And we've long had PvP achievements to complete in order to get the meta achievements for holidays. Most recently, there was the G.N.E.R.D. Rage achievement for Hallow's End and there's the infamous School of Hard Knocks for Children's Week.
Many PvE players roll on PvE servers and only want to participate in PvE activities. If they wanted to PvP, they say, they would have rolled their characters on a PvP server. Personally, I like both PvE and PvP but I must say, I don't like PvP mixed in with my otherwise PvE activities.
On the other hand, I love PvE activities mixed in with my PvP. For example, I loved the old Alterac Valley, where you had time to complete all of the side quests in order to launch the big bosses for each faction. I know that battleground could take hours, but it was a blast to play. I would love to see a BG like the old AV in a future expansion.