Argue about the timing if you want but a 20 team comp is just about a certainty
If/when it gets to 20 it will most likely be 3 of Perth, PNG, NZ2 (Christchurch or Wellington) or Brisbane 3. So one of those will miss out plus Adelaide, Christchurch/Wellington, Auckland 2, CQ, Sunshine Coast, Melbourne 2, Bears etc. Not impossible to see it going past 20 with decent options still on the table assuming nothing changes and relocations remain unlikely.
In theory with a few international teams and decent pathways all across Australia, NZ & the Pacific the NRL having 22 or 24 teams is not out of the question. Compare to main rival AFL who will go to at least 20 with teams all in Australia, players all from Australia and much larger squads.