I don't really know where else to write this.
I have heard some rumors that Horizons will be going all PvP all the time. Iv'e also seen some very good ideas on how to handle PvP.
Here is another idea:
Players default to be in a state of non PvP just like they are today. I am suggesting they have to go talk to a NPC who flips the player's state to PvP. This allows the player to cast spells and attack other PvP players anywhere any time. It also keeps those who don't want to participate in PvP, out of that type of action. Because non PvP characters can't be targeted in combat.
Another NPC could change a PvP character to a non PvP one.
This will prevent someone who just wants to play the game or craft or what ever, from being ambushed.