I don't think there would be a major issue with the opposing sporting codes IF Australia did happen to land the WC. From memory the AFL and NRL were all for the bid as there was a clear understanding what it would mean for the nation including the growth of the game if a WC was hosted.
Blatter knows it's a big mistake holding a WC in Qatar due to a number of reasons pointed out already but I think Australia is an ideal candidate in future. Stadiums are not an issue and certainly not the weather The game has devolped like crazy in the last 3-4 years.