Is it possible to add region or religion-specific executions? e.g. If you have bloodthirsty gods doctrine and pyramids or lunatic you could use "Drain of Blood" execution; If your character is of Greek or Sicilian culture, you could use Brazen Bull execution. If your culture is related to horsemen, you could have someone pulled by horses (either pulled apart by two or more horses running in different directions, or tied to a horse naked and hasting the horse so the victim is dragged on the ground behind the horse).
Also it would be interesting to have a chance to survive some of the executions (e.g. in a Trial of Gods execution, granting you the Witch characteristic) but that might not be feasible with the current mod support.