Not saying I disagree with you or that it's not possible to implement, just noting that there potential for abuse is there. Look at the Vote Kick option and how that was abused.
Scenario: FC group of 6 picks up 2 PUGs with a "Greed party." Let's say the two PUGs are healers and both are after heal gear. Prior to opening chest, group votes and allows say one of their DPS to change to heal who then rolls need. It's really not that far-fetched...