I'll add my two cents. My ideal 18 team comp would look like:
Firstly, 5 interstate/NZ teams, they are easiest:
Melbourne Storm - OzTam capital
Perth Reds - OzTam capital, unique timezone
Canberra Raiders - Major regional centre in ACT/NSW, National Capital
Auckland Warriors
NZ2 licence - 2 NZ sides uses timezone every week, creates derby in NZ, more opportunites to eat into RU in NZ. Population is there for a NRL side outside Auckland, nailing down where exactly is the harder part. Wellington probably, taking games elsewhere.
Adelaide not ready.
Queensland:
Gold Coast Titans
North Queensland Cowboys - Cairns/Townsville regional centre
Brisbane Broncos - City licence metro area
Ipswich/Logan - Southern suburban belt, metro area - new stadium
Brisbane North/Sunshine Coast/Redcliffe - Northern/coastal belt, metro area - Cronulla or Manly relocation - new stadium
Now the bit that will p!ss a few people off... NSW.
Newcastle Knights
St George Illawarra Dragons - city southern districts plus Wollongong - partly metro
Central Coast/Northern Sydney Bears - northern districts plus CC - partly metro (basically what the Northern Eagles should have been)
Sydney Roosters - CBD/Eastern Suburbs
Parramatta Eels - Geographic centre of city
Wests Tigers - playing out of ANZ rather than SFS for 4 games. Otherwise as is.
Canterbury-Bankstown Bulldogs - ANZ fulltime. Only team that has really made that joint their own. If they were to part time share with a Liverpool facility with Wests that would work too.
South Sydney Rabbitohs - but shifted back to SFS
Sharks, Sea Eagles and Panthers to merge or relocate where apropriate. Panthers junior areas absorbed by Parramatta/Wests. Sharks areas absorbed by Souths/St George/Sydney.
If we went to 20 team ideal comp, I'd have
Penrith Panthers and one of Cronulla Sutherland Sharks OR Manly-Warringah Sea Eagles. One to relocate, or retain both with no expansion on Central Coast.
With the Rabbitohs, Roosters, Tigers, Eels, Bulldogs playing partly at SFS/ANZ/SCG I'd come to some sort of membership ticketing arangement for games between these clubs. Dragons every second year (ANZAC host) too.
EDIT:
I'd also have the 4 South Queensland clubs playing at least 2 games each at Suncorp to get a Brisbane city ticketing/membership derby structure. Titans, Broncos, Ipswich-Logan and Sunshine Coast. 1 Big central stadium and 3 satellite 27-32k venues.