If youre doing a system purely for a way to create a schedule, then you can have divisions rather than conferences. A division can be anything from 4 teams.
Eg, in a 20 team league, say four divisions of five teams. They play 8 games H&A against teams in their own division, and then a single game against the other 16 teams. Total 24 games. Each year they rotate H&A against the non-division games.
You "could" make it the division winners from each make the finals (4) plus next best four teams record wise enter finals. Or just best eight teams.
Natural rivalries and/or trying to regionalize each division would be the usual method for devising divisions. But you could also split up each division so there's a mix of regions.
Eg, each division could be 3 nsw, 1 qld, 1 "non". As more qld and non teams enter league, it could then be each division is 2 nsw, 2 qld, 1 non.
Or you create divisions of four/five purely on close proximity and/or traditional rivalries.