Pharmaceutical drugs have patents of about 17 years (they often can drag it out for a few years longer by manipulating the way their drug is sold or just messing around with the law). Literature and other forms of art also have an "expiration date" on their copyrights--but it's typically 70 years after the death of the creator.

:/ Even seventeen years is too long of a time frame for us, and I sincerely doubt that manga artists would ever agree to anything like it, even one of seventeen years, because asides from a few famous guys most of them struggle and put a huge amount of effort into their work.