One of the concerns I have about opting in or out of PVP is if player A opts in and has a friend or two who opt out, I don't want player A's friends healing and buffing him when engaged in PVP.
Although we don't have many details yet, I think the concept is that only people with the same options as you can be in the same server/instance with you. If player A has full PvP options but player B doesn't, then players A and B will not meet. Player B will not heal player A since they will be in different servers/instances.
That is something we've discussed, and I'm sure they have discussed at great length internally. How do you handle that system? I want to game with my friend but he is a pvper and I'm not, now we can't play together? So they have some different options. 1) they can make it so the only PVP opt-in opt-out scenarios are, you either go in to a pvp area or you don't, or you accept a quest or you don't. At which time you simply can't see that other person if you aren't on that quest with him for being in pvp. 2) They can make it so you can still see people on your friends list even if say one is in a Guild flagged for PVP (A guild war), however once another player engages them or vice versa you can no longer target your friend with anything. Also obviously since you aren't pvp you can't target his opponent. Other issues this might cause is you can portal him out of danger, so you make it so you can't enter portals when engaged in pvp. (assuming that is an option, there have been talks that portals and recall will be in game, but not the details) That's all I have for now.
Because the game is instanced, they can make it so none of these situations ever happen. They can have: 1) No PvP 2) FFA PvP (kill anyone any time, no karma) 3) Faction / Guild / Team PvP (i.e. every side has opposing flags with no friendly fire possible, like WoW) 4) Karma PvP (like early UO / Lineage2) 5) Some hybrid mess They can have zones and / or instances within zones which have any of these rules available. In any karma based system (4 or 5) the rules enforce who you may attack, rather than who you can attack. The rules get tricky. There are always exploits. Heals, buffs, AoEs, cc / DoT / debuff + die to mobs, pulling guards, etc. Having played everything, I would never do karma based PvP again. They're welcome to put it in, but I suspect that if they do, you can avoid it. There's just way too many exploits and adverse incentives.
I think others have answered this, but just to state in a different way. Think of multiplayer like a matchmaking game like Halo or Call of Duty. When you enter a Hex you are matched with other players. You will not see everyone: just the people you are matched with. Thus, if your and your friends have different PVP settings you will not see each other. The exceptions would be in "safe areas" like towns where PVP will always be disabled. As such, your concerns should be eased as the scenario you reference will never happen.
I actually find that picture pretty awesome. Anyone outside of the fantasy genre or a NORP would look at that and be like wtf? I wonder if Gygax and his partner ever sat down and really considered the ripples they created and what they ended up being in the whole scene. I doubt we'll see much of that though OP. I'm pretty sure things like that will flag someone's healer to you as well. At least lets hope so
Keep in mind PVP is supposed to be Opt-in Only, and they want people to be very aware that they will be opting in. So if someone were to heal it would need to bring up a warning message with a nice big red PVP ACTION are you sure you want to continue engaging in pvp? Otherwise griefers would find ways to exploit that like they did in UO. (have a friend attack me, then I ask someone for a heal, that makes them gray to my friend who can then PK them without a murder count)