If both NZ & Australia get 60% plus of their populations vaccinated by end of this year - and everything suggests they will - high chance that quarantine free travel between the 2 countries will be possible. With health passports, proof of vaccination or whatever.
Bearing in mind that if the 2022 A League season becomes a pure winter comp, it won't start until Feb/March 2022, ie 12 months from now.
This is an estimate on when countries will reach 60% vaccination coverage (hopefully no new vaccine resistant variants in that time)