See Roy Morgan's research here.
The A-League's numbers are from last season. But it shows it is up there with Pay TV penetration - AFL Pay TV = 2.3m, NRL Pay TV = 1.3m.
If and when Australia wins the 2022 World Cup, AFL free-to-air of 6.6m viewers will be under threat.
For $950 you can get A-League viewer demographics. Let's hope the clubs and FFA are accessing this data. I assume they are. It would be good to see more of this data reflected in promotion activities and long term planning.