I agree, it has to grow organically. I think there are rivalries everywhere; local competition levels (neighboring towns), regional levels, interstate etc. I would expect there would most definitely be some form of rivalry between Nth and Sth NZ.
I'm not saying any rivalry will grow into what SOO is today; but we at least have start development of other ideas at some point & then set the stage with a few different trials and see how it goes. We can't expect that a group of VIC born RL players are going to get together unofficially, and challenge WA to produce a team of locals to start playing against once a year, or can we??
I think it's essential to get other comps started if we want to protect the SOO idea in it's current form (NSW/QLD only); there's already too much bypassing and rule bending to try and get the best players into the game, regardless of where they come from or where their allegiances originally lie.
However, if you don't really care too much about the original concept of QLD grown vs NSW grown (which is pretty much out the window now anyway); and you just want to see the best against the best, then open it up to everyone. The competition then simply extends out to who can sign the better players, QLD or NSW.