I also wouldn't hold Scotland Football as a bastion of professionalism, they have severe financial problems, and are at a level where they have fewer Scottish national players in the entire league than the Phoenix has all whites, in fact most of their squad comes from the championship in the UK.
So despite it being the number one sport in an area with a similar (but denser) population, plenty of history, and and a dedicated fan base there are severe problems with finances and the quality of the football.
The best we can hope for football in NZ is to have another team or two in an expanded A-League in the distant future.
I agree that the best vehicle for professionalism in NZ is the A-League. It's so obvious. All the hard work in setting up the league has been done, it has critical mass and it's in a much larger market than NZ. It's also a known quantity for new entrants and the risks are low. From NZs perspective the growth of professionalism here can also be managed in a much more measured way - club by club rather than trying to turn the whole ASB Prem pro at once. The only real disadvantage is a loss of "sovereignty", but who really cares about that compared to what we currently have? We're talking about a sports league not the economy.
The idea that the top tier of a sport in a country needs to be a purely domestic national league is at best, unnecessarily restrictive, and at worst, xenophobic.
That, in turn, clearly positions the ASB Prem as an amateur development or feeder league to the A-League or other pro leagues. The only casualty might be the CWC (the only real consequence of the sovereignty issue) but the lost revenue wouldn't actually be a big problem if we got the player payments problem under control (and I'd back us to still do quite well anyway).