This could easily be abused unfortunately. I did a run the other night where I paused for like 5 seconds to use the dragonstone or whatever in the dungeon, and the group started the fight killing me by creating the fire barrier. By this system, I would not be eligible for loot because I was killed by my own team starting the encounter early.
I could see people exploiting the same system by engaging bosses quickly to kill off other members before the fight begins allowing them to be the only ones eligible for the loot. Especially in instances where they majorly over-gear the content and are farming for crafting mats - running ahead while loot is being voted on and starting the next boss encounter to put up the barrier and prevent the other players from contributing.
Vote Kick is a preferable solution, but also exploitable in the above situations, though it's not quite as easy to exploit. If you already have 3 buddies to join with you to exploit the system, you could probably just run the dungeon without outside assistance anway.