I don't think there will ever be a major competitor to Sky as they wouldn't be able to afford major sports events without a large subscriber base and it will take years for the sports rights to expire.
If there was more than one pay TV operator you would probably end up with multiple set top boxes as different sports rights might belong to to different channels. In the long run it might cost you more than one monopoly operator.
People seem keen on Foxtel but when I have looked at their website it actually seems more expensive than Sky.
Just my 2 cents worth.