EVE-Online has this feature, during their annual tournament, but I do not believe it is open to everyone.

We will run into issues of 3rd party calling out shots/hints/3rd eye for the active parties involve, especially in PVP. One possible solution to this may be a 5-10 second delay, like they do with TV shows in term of *beeping* out words. I can see this be a neat feature for PvP arena.

For raids, I dislike the idea of the party leader having any control on who can and cannot watch. Only control the party leader should have is either allow or disallow spectator. Again, I would also consider doing this with a 5-10 second delay to prevent some of the "helping hand" issues some have already voiced.

jc