At 30,000 members I would strongly doubt Labour and National would currently qualify either!
Labour's reportedly got over 56,000 members. Cannot find figures for National, but you may be right that they won't qualify.
That total of 56,000 includes affiliated unions. I am not sure if affiliated membership should count in terms of actual, signed up party members. My guess for both Labour and National is less than 10,000 each of those.
So we'd quite likely end up with a situation where nobody could stand list candidates. How would that benefit the country?