I would also point out that Dogecoin's stated purpose in this move is to stabilize the currency at 100 billion coins. They believe that 5 billion coins fall out of circulation each year; therefore they intend to mint 5 billion new coins to keep the money supply constant at 100 billion coins.

Therefore the Dogecoin money supply after 2015 will be constant: the number of coins in circulation will remain approximately 100 billion, and the value will only increase or decrease as the demand for the currency moves.