For my pick, I'll take
NFL games, which appears to be valid based on the sports question in the sign up.
At it's peak, the NFL had 110+M people watch the Superbowl one year.
That's 1/3 of every living man, woman and child in the US.
In addition, the sport has been around for ~100 years, and even if we only take the years after they merged with the AFL, we still have 70+ years of football games to watch. MY viewership will include the 100k+ fans that go to games each week, but instead can now watch it on my service.
There's a good chance that the 120k+ people who have the NFL network will sign up, just as replacement for that. While we won't have the commentary from some of the major networks (Fox Analysts, CBS Analysts, etc would not come with the broadcast), we still have the games them self. Flagship program that will appeal to a huge portion of the American population.
The ability to rewatch any game you want, from any era is amazing.