Depends on how safe being King is likely to be...
But it does make me wonder if anyone ever turned down being King once elected? Or would that have been made known before votes were cast, if it were for whatever reason the case?
alot of people have, as a loyal vassal you have power and long-term security, becoming king is putting personal ambition above long term stability and power of the house. Godwin turned down the throne as he knew taking it would start a civil war, but putting St-Edward of the old pre-conquest royal house on the throne was the future stability option, only then he didnt have kids so it didnt work. End of the Anarchy, Stephen and Matilda agree to give up their claims on the throne, choosing Henry as the compromise.
And im sure not england has heaps of examples.
It would be very annoying if you couldnt play a loyal, powerful duke without being elected king against your will. Becoming King might lessen the power of a duke and his house as then he would be answerable and have foreign kings to worry about instead of just his well trained king and lesser counts. Why give up a strong and safe position for a prestigious but shaky one.
That happens in Sengoku and its very annoying, you cant play a vassal as every keeps trying to elect you and you cant do anything about it. You should be able to refuse nominations in support of legitimate candidates.
And having elective would allow you to conquer a kingdom but leave it to someone else, Rise as Leofricsson or the Wake, or invade as Malcolm Dunkeld to drive the normans out, rule for a generation then leave it to the Aethelings son, restore the legitimate king once the crisis has passed.
So its just vassals and rulers heirs? surely every in-realm claimant should be available for nomination, probably every claimant no matter where he is, be a king in exile in the varangian guard or fighting the crusades or quietly sitting in a university next to the capital all the way to the King of France, whoever has a rightful claim should be electable.
In the 1066 scenario start, Harold Godwinsson is king but surely if you get an elective succession, Eadgar the Aetheling should be a candidate. but hes not a vassal nor a relative but having a legitimate claim should make him an option.
Brother too, for 'stability from the dynasty but a need for strong, tested hands' situations.