Given people are putting their own ideas I will do mine, its a bit outfield but why not lol.
A-League expands to 16 teams in the next few years
Then for one season only all 16 teams play home and away, at the end of the season teams that finish 1-8 and 9-16 will form division 1 and division 2 which can be called the a-league football league in the following season.
The next season the a-league football league will consist of 2 leagues of 8 teams , the bottom 2 of division 1 go down, and the top 2 of division 2 will go up, therefore all 16 teams will have something to play for rather than a closed 16 team league h&a format.
Then the NSD can come right in as an option for the 3rd division similar to the JFA model in Japan or national championships in Brazil where it can be used to add more teams into the a-league football league where they can get promoted into division 2, once there is enough teams from both a-league divisions then you can add pro-rel to the NSD i.e the 3rd division. (The NSD could be called something maybe the NPL Championship?
The only dilemma is the number of games which division 1 and division 2 will play given they only be 8 teams initially, you can go 2 home and 2 away where it be a bit boring but would cover the season length.
Or an outfield option (probably not a popular one) is to have division 1 and division 2 sides to play one home and away as an 3rd fixture where division 1 sides can host a home fixture against division 2 sides, this can be an incentive for teams trying to stay up as they can get an extra home game in their season.
Division 1 and Division 2 can still have finals as it adds to more meaningful matches, they can be used for promotion, competing for the league and even for Aus Cup spots.
What you guys think?