I could see an extra order for stadlers from GA. It would make more sense than an extra mini fleet of Hitachis.Perhaps once settled in, NiN services will be for the next franchise with new Hitachi trains or an additional order for 745s although the by all accounts the Stadlers are a better option.
Currently just getting up and running is the focus, what's done is done in regards to the 10 intercity Stadlers / commuter sets.