I think things could go this way. We have one party (the Progress Party) which is quite populist and wants to reduce taxes; my impression is that they view the EV incentives as a crowbar to get rid of a lot of the vehicle taxes. But while the progress party is in a coalition goverment, they do not have the majority in parliament. The coalition government is dependant on support from the Liberal Party (disclaimer - I'm a member), and the Liberal Party values itself on being green. They've taken a firm stance opposing proposed tax cuts on conventional vehicles and gasoline, and will likely succeed in getting their way. This is a fight that is too important, and the Liberal Party knows it can get the desired result by ending support of the coalition government (tossing them out) and opting to work with the Labour Party. It's highly unlikely to go that far, most likely the Progress Party will cave.
The next parliamentry election is in 2017, so the Liberal Party will still be in a very good position for supporting EVs until then.