I think the hype over the wolrd cup is as much due to the "event" as it is the sport. For example i had a guy ring in and say "he was staying home to celebrate (after our draw with Croatia). He is Fijian-Indian and wouldn't know the difference between Kewell and Viduka, but he used that excuse.
I think there are two potential issues.
1. Soccer's potential to grow
2. Has Rugby League becoem stagnent?
Soccer is changing in this country, with the A-League, making the world cup and with more international competition matches becoming available (at least on Fox). More people are becoming more aware of more players. Also the increased numbers of females playing will mean more families may get into going to the A-League.
On the other hand Rugby League has gone through tonnes of changes in recent times, and now has sort of settled. Perhaps the inlcusion of the Titans will give some boost. But with the game so structured now that it has taken alot of the excitement out of the game. Look at the last 4 friday night games. all cliff hanger endings, but to those who don't watch lots of league, they probably switched off early because there wasn't alot of exciting play.
Then you have the weekend at Aussie Stadium where over 60,000 went to watch the AFL and 6,000 went to the league (which included free giveaway tickets). I don't think league will become extinct in a hurry. But if the corporate dollars drain out because they are taken up by AFL and A-League, then they could have a problem....