I think the Egyptian league should be the next added, if any, followed by some more South American leagues (those mentioned above) and maybe a few Caribbean or Central American leagues? The NZ and Canadian leagues are so poor that teams (Wellington Phoenix, Toronto) have emigrated to get out of them- although we have the Welsh league, I suppose!- so adding them to fill up their regions makes little sense. The other Oceanic leagues are really, really dire.
The Uzbek league is one that should definately be considered though
It's all irrelevant though, as SI have said they're happy with their current leagues and won't add any more.