A way to fix the new vault block

The new vault block was announced to give different loot to different players when given a trial key. Each vault block can only be used once per player. This is great in multiplayer so everyone can get loot, but what about singleplayer? In singleplayer, it's just another chest. How can it be fixed? Well, since Mojang has the code for player specific loot chests, why doesn't every chest in every structure get player specific loot? And then a new use could be found for the trial key, such as an unlockable vault room with 3-5 chests inside, or an unlockable boss room which drops a cool legendary item or weapon. Both these rooms would be unbreakable, so the only way to get in is to use your trial key (maybe even more than one?) Thank you for reading!