So, how would it change the nature of American government if every law came with a sunset clause, by default? In order to persist beyond, say, three years, they'd have to be re-adopted. I believe that the primary change would be to make governance more experimental and more fluid. Good thing? I don't know. I think most people are annoyed by the very slow pace of positive change in this country, but probably most are happy that the pace of negative change isn't any more rapid.
Would there be other significant unintended consequences? E.g. Regime uncertainty? Could those consequences be mitigated in some way?