Yes. Absolutely.
MMA is nowhere NEAR fully saturated. Tthere will never be another major MMA promotion is a tad short sighted.
It's of course possible. Are any of the major promotions today going to be that secondary promotion? No, probably not, none are designed in a way to do that.
As the poster above me said, there are a lot of TNA's right now. The UFC has a lot of blind spots and all it takes is a couple of crossover stars from social media to get people to at least try out other products.
Think of it like this, the WWE was the biggest promotion for decades and THEN in the 80s became way more popular than the UFC ever was (Hulk Hogan in the 80s dwarfs McGregor and Rousey) - yet years in WCW, which was as popular as Bellator became a viable commercial alternative and was even more popular than the WWE for a couple of years.
So yes, if someone rich enough wanted to make a promotion to challenge the UFC they absolutely could do it. Or it's entirely possible that an org in another region that has good capital grows their brand globally adjacent to the UFC. Even a place like France just opened up with in the last year or two. A LOT can change between now and 2032.
It's actually more likely than not there is going to be a second major MMA promotion. If MMA does become more popular world wide the UFC doesn't have the infrastructure or reach to consolidate all of that.
If MMA's popularity becomes insanely large in a timezone that is not friendly to American audiences think about how easy it would be to capture that market with the right finance and marketing. The only way this doesn't happen is simply if MMA's fan base never grows from this point forward.