In the original mudlib there was a gravestone each time someone died, it was time but they got annoying after some time
We could do a graveyard with zombies as monsters to fight against, like an outside-haunted house.
Player-built gravestones would be interesting too, may be a general 'memorial' stone or so? Where you can write on before it is planted, so you can read special text when right-clicking it. And only members of the same kingdom can destroy it.