It isn't just a question of whether NZ quarantine on arrival restrictions are lifted (seems unlikely for arrivals from USA this year), but other risks :
- being infected while overseas (with no insurance coverage)
- border/travel rules changing at short/no notice while overseas
- flight schedules changing at short/no notice while overseas
To me, this suggests booking as late as possible (even just days before you want to go); or take a lower risk option of domestic NZ (and probably Australia too after about July/August 2020).