As a suggestion for adjustment to the current scenario (fully expecting to get mauled on this, but anyway...)
Winter leagues are currently regional, or thereabouts... so what if there was an agreement that the best regional teams qualified each year for a truncated national league that started at the end of the season and ran through till Christmas... for instance, it could be say top 3 from north, top 2 from Central, and South Island champion... those 6 could then play home and away, Sept-Dec...
That way, the "must-be-a-club-league" obsessives would get their wish, the national league portion would potentially have lower overall costs, and perhaps a more marketable angle for things like TV coverage... there'd be de facto promotion/relegation as each year's National League would be qualified for from the winter... if the regions went for it, a "franchise" entity such as Auckland City or Hawke's Bay could play in their regional comp with a shot at making the Nat Lge... any club that backed itself to go it alone and take on the big guns could do so... and the bigger clubs/franchises would be able to assemble strong teams, hopefully meaning the standard would not slip too much, and may even increase a bit... and maybe a rule like you can sign 2-3 players who didn't play for you in winter but can play in Nat Lge...
This would also allow Nat Lge players to have an actual off season from New Year through to March-April, rather than the year around issues that some teams/players complain of... the top 2 from the Nat Lge can play in the following season's Oceania Champs tournament, and if they win, have a good run through winter and the Nat Lge to prepare for CWC in December... plus the Nat Lge part would be in (arguably) better weather etc... maybe even time a grand final for the New Year period when there's no other sport to compete with and the media will talk about anything... and play it at a holiday spot like Mt Maunganui or Nelson where you can promote to holiday people and get a decent crowd in (BBQs, bouncy castles for the kids etc)...
I'm guessing some may say this sounds too much like the former Superclub thing, and maybe they're right... am just thinking out loud, and perhaps it may even cost a little less than the current scenario, especially in travel...
Feel free to savage this to your heart's content... all I know is that people were whinging about how the National League was being run when I first started watching in the 1980s, and that still seems to be the case... I guess this is just an idea to try and meld the best of both scenarios into one cogent system... and I'm sure I've overlooked loads of vital and essential aspects, like financial rules etc...