In the current state of the server, I don't see a reason for the '4 toon rule' to exist; it simply punishes players who don't have access to 4 accounts, which has become more and more common.
Having said that, IMO this change would be priority #9001 relative to some of the other slated changes, since there are easy workarounds that are available for the very few players that run Hell with 3 or less toons.
While perhaps not ideal, the practical solution would be to just make a 4th account which you log in and invite to party right before popping the chest (IIRC the four party members don't even need to be on the same map? It might even work with Level 1 toons, not sure!).