How about 20? Or 10.
10 or 20 seem atrocious to me.
Under 10 years, the Last Wheel of Time book comes out and the first one is free a few months later, and the Dresden Files is out before being close to done.
Under 20 years Song of Fire and Ice is already out there without being finished.
I think people who make their money on creativity and artistry deserve incomes too. Even if its a cult classic that doesn't kick in for decades or they're a small timer who needs a lot before they add up.
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I sometimes wonder about a thought experiment where everyone checks either "IP abider" or "No IP Laws". If you pick the former you have to abide by them forever even if those who check the later don't. If you check the later, then nothing you ever make ever is protected by them and no company that checked the former can hire you.