What bugs me about nobles is that they don't accomplish much from a either a gameplay perspective or a simulation perspective.
Gameplay speaking, you're effectively handing players an antagonistic, unappeasable force. Nobles are never content; even if they have 300 adamantine statues, they WILL continue to demand more. Even in less extreme cases, a perpetually demanding and altogether useless character doesn't do crap for the player. In the best case, they do nothing. In the worst case, they kill the dwarves that do stuff.
I don't like the solution involving punishing people that try to do away with them. Punishing players is never a good thing, really. It just frustrates them, and makes the game not as fun.
On a simulatory perspective, if the nobles are going to make demands and mandates, they need to be based on something besides their whims. There is no logical reason for someone with 30 Rose Gold cups to demand 3 more every other month. Not only is it repetitive and either stupidly easy to accomplish or just outright impossible.
I'd say the solution needs to be that nobles provide benefits, that while not really critical for playing the game, would seriously help accomplish tasks in a much more streamlined fashion. Kind of like the old version's various houses. I'd even use them to allow fortress specialization. In your nobles menu, you'd get a list of nobility for your current fortress level, which would give you various demands, such as 'build x number of workshops', 'get x legendary warriors', or 'engrave % of the fortress'. Once you choose a noble to appease, they'd arrive in your fortress and confer new advantages, such as being able to train your men, order specialized equipment from the mountainhome, or whatever. The noble would occasionally confer tasks based upon your fortress, but would stop if you managed to get everything 'perfect' in their eyes. This would make nobles a goal to work towards, and the player would be rewarded for accomplishing the goals, instead of punished for failing them. The player would also take better care of the noble, both because they worked to get it, and because it gives advantages for it's presence.