One of the most interesting elements in Battle of Azeroth is that Blizzard is doing away with PvP and PvE rulesets for different servers. Instead, any character on any server will be able to flag or unflag PvP in a major city. Then when they go out into the world, they will be (seamlessly) put into a cross-realm zone where everyone has the same PvP state.
This is a really interesting way to handle PvP. Limiting changing state to major cities encourages people to try out world PvP. If they decide it's not for them, it's fairly painless to switch back.
There are also lots of interesting things Blizzard can do with this system. For example, they could ensure that each PvP cross-realm zone is balanced between Horde and Alliance. It won't be like modern PvP servers where one faction outnumbers the other ten-fold.
Blizzard could also eliminate ganking entirely. Simply put the max level players into a different cross-realm zone than the lower level players. Absolutely unfair fights simply can't happen without the players forcing it through grouping shenanigans.
About the only major loss I can see is that PvP fights at raid entrances will probably go away. It would be very likely that a group intent on raiding will unflag before heading over to the instance.
All in all, I think Blizzard's plan for PvP is a good one, and it will be very interesting to see how it plays out.