I have a suggestion for a "smart loot" system where the game would be able to detect drops in people's inventories/armory chests etc. to determine drop rates. If no one had a single drop in your party the drops would be 100% random. If lets say a player in your group had a specific drop, the next time you did that raid, the game would detect that one player currently has that drop. This would slightly lower the chance for this item to drop again. The drop rate would decrease by maybe 1-2% and would be distributed between the other drops in the chest. The more players with a particular drop would further decrease the drop rate of this item. The drop rate could never reach 0% however if all 8 players had a particular item then the drop would be significantly lower than the other items.

This would keep the RNG in place while slowly decreasing the chances of seeing a duplicate drop 4 times.