That isn't necessary. There will already be plenty of coins in circulation, and miners already have an incentive from the transaction fees.
The protocol makes a promise. People make a choice based on that promise. Why would you change the promise after the system is already widely adopted and used and shake peoples faith in it? Regardless, it would require near unanimous consensus to make such a change without splitting bitcoin into two separate and incompatible currencies. Like I said, "The difficult part is convincing everybody to use your new protocol."