When a work is copyrighted, the creator can grant a license for others to use the work. What if the creator has not completed the work, but wishes to sell licenses that would take effect after the work is completed?
In the U.S., you can make a contract to sell just about anything in the future. Sell away. Unless its people, don't sell those. Or financial instruments; don't sell those either without filling out the right forms. Just know that if you don't deliver what the contract says, people generally want their money back.
People preorder video games at stores all the time.