We really are spoilt for choice, whilst Brisbane 2 and Perth seem the obvious ones for next round after that you still have NZ2 (several options), Adelaide, Brisbane 3 as good options. CQ, PNG, Central Coast, NZ3 and Melbourne 2 as unlikely but not totally impossible options as well.
Brisbane 3 is just a really bad idea for the foreseeable future...
Don't get me wrong I'm sure that Brisbane could support three teams and stuff, but that is beside the point. The real question is does the comp really need 3 Brisbane clubs to get the best results out of Brisbane, and I'd argue no it doesn't.
I'd argue that there're limited spaces in the comp so another market would have to miss out so Brisbane can have three clubs, and that adding a third team in Brisbane would largely just be cannibalising the other two clubs fan-bases to have a third team cause we can, and at that point you're just trading two big clubs for three smaller ones which is a dumb idea.
Brisbane2/dolphins. Yes
Perth. Yes
Adelaide. Yes relocation of Sydney team
Why relocate a club to Adelaide?
I mean for a start do you really want a club that has failed in a market like Sydney at the head of such an important expansion project?
CQ. No small population
PNG. No dangerous poor 3rd world country
Central coast. Yes relocate either manly or the roosters
NZ2. Yes Christchurch
Melbourne 2. No
It may not happen in the next 10-20 years or whatever, but a second club in Melbourne is inevitable.
It really isn't a matter of if but when it happens, I mean in the not to distant future Melbourne is going to have a larger population than Sydney, and as market (in the sports market in particular) it's importance in the Australian context is only increasing.
I'd even suggest that the NRL should look to do a long term GWS style expansion project to Melbourne where they bankroll the club for 30+ years to establish it now so they can have a solid presence in Melbourne going forward to preempt those cultural shifts that are happening in Australia as soon as possible, but the NRL has such a shitty spread of teams in the comp population wise that it simply wouldn't be sensible for them to undertake a project like that while places like Perth, Adelaide, and multiple cities in NZ don't have clubs... It is what it is I guess.