I've heard mention several times; quests that flag the player for PvP. Will these same quests be available for single online and friends only online? I would hope not because it defeats the risks reward purpose...why do the quest in the online open world when it can be done at no risk? I hope that the online open world has options not offered in the other modes. Something to entice people to take risks instead of just playing with friends or by themselves.
I think the quests would be optional and probably have some nice carrots to make those that don't like PVP to consider it. If in SPO mode I doubt another player would come in, but an NPC might be there to bar your way. However, probably better not to show any PVP type quests if you are in SPO mode.
I think they could and should be displayed in SPO, just with prominent warnings of the potential consequences. After the first offering, a check box could be provided saying "Do not offer this quest again". That will permit the SPO player willing to take the occasional risk to do so, and those who want nothing to do with it to opt out.