NRL needs at least 6 teams pulling in full/to close houses.
I think it's heading towards 6 teams pulling 20k again. It's all about memberships.
The teams that have potential to do it -
Broncos - avg 34,300 - could do 40,000 regularly
Bulldogs - avg 22,412 - could do 30,000 + regularly
Titans - avg 17,400 - could do 20,000 + regularly
Storm - avg 15,271 (despite everything) - could do 20,000 + regularly
Knights - avg 13,768 - could do 22,000 + regularly
Cowboys - avg 14,830 - could do 20,000+ regularly
Eels - avg 17,320 - could do 20,000+ regularly
Rabbitohs - avg 17,196 - could do 25,000+ regularly
Dragons - avg 16,900 - could do 21,000 + regularly
Roosters - avg 16,600 - could do 20,000 + regularly
Tigers - avg 17,800 - could do 20,000 + regularly
In fact, all these teams have already done it, proving that the support is there.
If larger games are scheduled for bigger venues and are promoted well and memberships increase, it is possible for the game's average crowds to break 20,000 in a few years. When you take into account games like the Eels v Bulldogs that drew 33,000 should be drawing 50,000 you can see there's enough there to get over the line.