The males ages 18-34 demographic will always be at the core of the UFC's viewership, but there's a second graphic that's also crucial to focus on: children.
While some might scoff and be perplexed at directing the sport of fighting towards children, the shift in the UFC's audience will happen organically over time.
Think about the majority of UFC fans. They are males ages 18-34. The UFC started to explode in popularity with the debut of The Ultimate Fighter in 2005.
The fans who were 18 when TUF debuted are now 25 years of age. As the passage of time continues, the MMA fans of yesterday will not only still watch the sport, but will also create the MMA fans of tomorrow by having children.
Having children be avid MMA fans might seem like an abhorrent thought to some, but sentiments like that will fade in time.
To the older generation(s) of Americans during the rise of the UFC, MMA was something weird, alien, "savage" and scary. They preferred boxing.
The current generation of youth will not have such ideological baggage when they are the next generation of oldsters. They will have grown up as MMA fans or at least exposed to MMA in some capacity. The sport will therefore have a baseline level of acceptance in society and having kids watch it won't be seen as a grievous parenting error.
Thus, as time goes on and MMA fans plant their seed (or spread their legs), the number of kids who will see MMA by virtue of their parents being fans will increase. As this happens, the child demographic will become of greater and greater importance until it can no longer be ignored.
Given enough time and enough MMA fans having babies, the child portion of the UFC audience will increase, and the UFC champions of the day will become akin to what famous professional wrestlers were: cultural icons and heroes to children in every sense of the word.