I find CK2 wars overly simplistic there is only "winner takes it all", "pittance for a successful defender", "reset to status quo". At the same time, I reckon EU4 type peace would be an overkill. Instead, I think Paradox should take inspiration from Vic2, that too has casus belli-linked demands, the difference being that in Victoria II, more war goals can added during the war.
E.g. you declare war with the casus belli to conquer a duchy, you are winning, but during the war, a claimant from the enemy kingdom appears in your court, you now have the option of adding "install X" as an additional war goal. While that decreases your existing war score if you win not only get your duchy but a potential ally.
From the defender's point of view, instead of just making white peace, they too can add war goals. Also, when making peace, instead of just choosing to accept or deny all demands. In addition, the second party might accept certain demands but reject others until certain war score been gained.
E.g. you declare war with the casus belli to conquer a duchy, you are winning, but during the war, a claimant from the enemy kingdom appears in your court, you now have the option of adding "install X" as an additional war goal. While that decreases your existing war score if you win not only get your duchy but a potential ally.
From the defender's point of view, instead of just making white peace, they too can add war goals. Also, when making peace, instead of just choosing to accept or deny all demands. In addition, the second party might accept certain demands but reject others until certain war score been gained.