I suspect 'combined' teams would make up a very small number, maybe 2 or 3 (Latin America, Africa Utd, Scandanavia?) out of a hypothetical 16. I don't see the harm in them in a comp where the main focus is developing the game moreso than winning. That said I'm sure teams like Serbia and Canada would have a big crack at winning it.
I know Latin Heat was planning on entering as a once off, then splitting into individual nations permanently.
I wouldn't support LH entering the actual World Cup as a combined entity, but there is precedent of composite nations in international sport. At the development level of RL I think you have to be kind of petty to care.
Anyway, back on topic - even excluding the few combined teams, there are more than enough teams that would be interested in competing in this kind of competition. Personally I think it's disappointing it won't go ahead.
So does this guy
http://www.theroar.com.au/2017/02/06/time-right-rugby-league-world-cup-expansion/