We don't really want to incentivize people to use duplicates when other reasons apply. I would love that all close reasons behave like duplicates close reasons. If I can be trusted to know that two questions are the same, I also can be trusted to know that a question is unclear, is not withing the site defined topics, is too broad or opinion based.
I don't really want the system to be more complex than it already is, I want to know that if I cast my vote I know exactly what will happen: either the question is closed or my vote goes towards the pool of votes. Being surprised that my close votes behave differently in different context makes zero sense to me. If I cast a vote, wherever I cast it I want it to behave the same way.