That's simply brilliant. Did you come up with that yourself, by the way?
I think that people could be persuaded that this should be a fundamental principle like democracy or free speech. It sufficiently meta that it wouldn't carry a lot of political baggage. For example, a person who ardently supports a particular law might accept this 80/20 principle even knowing that his favorite law could get stuck down.
This idea should be given a catchy name so it can spread as a meme.
My own wish is for a "balanced budget" amendment for complexity: the government gets a finite amount of complexity they can spend on laws & bureaucracy, and to enact more laws they must first remove others. But you'd need a way to quantify complexity. Your solution is much more practical.
Then we would prevent most new useless laws.