I think this might be a practical fix to the problem everyone has when trying to get the PvE content in Cyrodiil done. But already I can also see this could be abused, so I'll do my best to address that too.
I recognize that Cyrodiil is the big large, "Don't Go Here If You Don't Want To Die" zone that is mainly for the Alliance War PvP aspect of the game. Players go there to play against other players. Yes that's all well and good. But Zenimax had the idea to also include PvE content within Cyrodiil. Now unless you're one of those god-like Vet16 players who can handle unwelcome interruptions during a Delve, Quest, or Dolmen, the majority of us left don't care to be ganked while in the middle of a boss fight. And then are forced to travel all the way back to start over again, that is, if we're not ganked on the way.
One possible way is to add another feature to the Campaign menu. To enter one as a Neutral Character.
In this instance, your character is now untouchable by enemy faction PvPlayers and they themselves are untouchable by you. You are now free to roam about the cabin and do your questing.
However, being invincible can be abused in a PvP area. An idea I just thought of was to act as a spy for your guild/faction. Perhaps you enter your guild's campaign as a Neutral player and then go off to an enemy Keep to get a read on their defenses and movements. Suddenly your guild knows exactly where and what the enemy players are at and are doing. To fix this, Keeps can have a no-go zone applied to a certain radius around them. If a Neutral player decided to get a bit too close, then you'll end up just like if you decided to wade into Slaughter fish infested waters. A very, very hard hitting arrow to the knee.
This way PvP players can't be taken advantage of, and players who just want to get the Cyrodiil PvE content done won't be harassed.
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