2 easy merges to pick imo:
Sharks and dragons. More ppl in the shire go for st George than sharks anyway. I grew up in Gymea Bay. My whole family apart from me go for dragons. It's because dragons were around a lot longer before the sharks. So dragons was the most local team for most ppl in the shire, for a long time. And were very successful for a period before the sharks existed.
Also dragons covering st George and Illawarra regions, its all adjourning the shire.
Next would be titans and Broncos. I live on gc now so know there are more Broncos fans here than titans fans. Same reason as dragons support in the shire. Broncos were around a lot longer than titans. And Broncos have been pretty successful too for a long time. Nobody would care if titans were absorbed by Broncos. Broncos already own se qld.
There is no way the Bronx will merge with the Titans. Titans don't bring anything to the table except juniors, but Brisbane have the best nursery already. They'd rather Titans die. Them dying is essentially a takeover anyway.
Where will a Gold Coast junior fall under without the Titans? Not Newcastle or Nth QLD. Will be broncos by default. Them dying is the takeover.
besides, NRL would never approve a merger even if broncos were feeling generous and ignored my above statement. NRL want to break that monopoly, not strengthen it.
now that I think about it, my point also applies to Cronulla. They die, St George step in anyway. Like you say, they engulf the area and have a sizeable chunk of supporters in the shire anyway. The only way around that is if Cronulla get VERY spiteful and give the territory to Souths. That episode be very nasty and hard on the juniors but I guess it's possible, but it wouldn't be worth St. George's time merging and Souths won't merge no way, I will not let that happen!
I actually think Cronulla are in trouble, I really think the NRL are more than happy to let them fail.
It makes the territory of St. George less complicated, it shaves a Sydney team off which they are desperate to do, and they aren't profitable. Low fan base.
Cronulla-Sutherland future would be much better suited as a feeder team to Souths operating from NSW cup, or a relocation to CC.
That's if we have to kill.