If it suddenly stops selling after December there is this possibility.
looking at western markets, somehow i think while 2015 will be an obvious decline (like 2013 -> 2014 for 3ds), it won't be the system falling off a cliff (like 2013 -> 2014 for vita). part of this is that the system will be supported more regularly throughout the year with software (albeit smaller releases than the likes of mario kart and super smash bros.). 2016 should be when the wheels come off.
3m for japan, 5m for us, and 3m for europe sounds right to me.