i totally agree with Hemanth, naruto will unlock the rinengan near the end of the series. the reason for this is because if any you remember, the requirments to get the rinengan is to have both the body of the sage (yang) and the chakra of the sage of the six (ying).
now, the reason why i say naruto WILL unlock the rinengan is because naruto has the Body of the sage of the six (yang) AND if you all remember itachi gave naruto some of his power (ying). now as this moment im writing this, naruto has the capability of unlocking the rinengan BUT the only time he will unlock this is when sasuke dies. sasuke and naruto will fight each first, then they will end up both fighting madara, when the happens madara will kill sasuke and that when naruto will unlock his rinengan. naruto will use his rinengan to revive sasuke........(just think about this for a second, even if u don't believe this, it all adds up). maybe i might be wrong about the ending part when i sed sasuke will die BUT, im about 90% sure that naruto will unlock and gain the rinengan