Light and Void meeting together makes them explode - I believe that them clashing together is what formed the universe that Azeroth exists in - so trying to put both together at the same time would likely end very poorly for a priest.
Gameplay can often be a decent guide to lore but be careful not to take it literally, because the game often makes compromises on lore in order to make gameplay work.
Easy example, you can play as a Lightforged Shadow Priest in-game, despite that…probably not Being A Thing. I used to write paragraphs about how taking gameplay literally meant that a random wasp from Zangarmarsh could kill the entire Defias Brotherhood on its own but now that all zones scale I can’t do that
Btw, I agree with all that has been said except that Anduin mass resurrected anybody. It was
a holy barrier that healed the wounds, not some mass ress thing.
The visuals of the BfA trailer seem to be flashiness for sales rather than what actually happened, seeing as Sylvanas never leaves the wall in the actual ingame siege and Andy doesn’t revive a single soul, instead having us players run about to heal them while he shields people.
Finally decided to go look this up, because I honestly seemed to recall the same thing. And yes - they can touch just fine, so long as Alleria isn’t all voidy.
https://i.imgur.com/f3J8ZTt.png
Curiously it appears to only be Turalyon on the receiving end of the pain. This was also the case in the ‘Thousand Years of War’.
I also remember it from the book, and one more thing we learn from it is that LF can take a void portal with seemingly no issues except an unpleasant experience