when I really think about it, probably less than 50% of my friends really watch sports. When you throw in their wives, the numbers go down even further.
So out of the 6.1 million Mormons, how many of them make it a point to watch sports of any kind? 20, 30, 40%?????? Then out of those, how many are fans of other schools? In Utah, there are many LDS people like me that cheer for the Utes and other teams not named BYU. Out of state, I am sure a lot of LDS people cheer for their local teams (for instance my LDS relatives back East all follow local teams, not BYU)
To truly have a national presence, not only will BYU have to convert a majority of those LDS who watch sports, but also get a lot of Non-Mormons to tune in. The LDS numbers in the states is just not very big to begin with.
But if BYU is successful, they could have a mini-Notre Dame affect. One where they attract not only their fans, but fans of other teams who tune in simply to cheer against them.