A few years ago, Rupert did say, " we've always preferred Aussie Rules". And the News Ltd CEO backed him up. My theory is, once the AFL has enough subscriptions in NSW and Qld, then Fox would ditch the NRL. IMO, that's where Fox is working towards.
For many years, Fox wanted every sport. But rights deals are becoming expensive. In recent times, Fox have let go of Super Rugby, EPL and the A League.
Currently, Fox to their chagrin, still needs the NRL for it's subscriptions in NSW and Qld. Also those same subscriptions could be partly funding the AFL deal.
The NRL needs to be fully aware or assume of Fox's long term intentions, otherwise the competition may become second rate.