In a recent Instagram Q&A, Kailah stated that she wouldn’t be doing another season of The Challenge main series.

We last saw her on Total Madness, and that season was pretty tough on her. Not only was she shoved into a dark bunker, but she also ended a relationship and was called the “foulest” woman in the house.
But that’s not her issue; it’s the time commitment. The main season of The Challenge can take about 3 months to film, especially if a quarantine is involved. This is double the amount of time it would have taken during the Invasion era. Now that Kailah is engaged, this would be too much time away from her regular life.
Kailah also said she “might pop up somewhere,” alluding to All Stars 3 of course.
So, which girls from The Real World would actually do the main series? There’s only a few.
Nany is the most likely. She’s in a relationship with Kaycee, who is still invested in the show. So, there’s nothing holding her back from going.
Aneesa is still friends with the Nany, Josh, Kaycee, and Devin crowd. She’d participate if asked, but there’s a possibility injuries could prevent her.
Ashley M. would likely participate, but after getting “deactivated,” production might not be interested.
Nicole Z. is a contender. She doesn’t do every season, but she seems willing to come back and risk another injury.
Anyone else would be a wildcard; most people are more interested in doing All Stars. Jenna might have interest, but she has her baby now. People like Sylvia, Jemmye, and Marie did seasons a few years ago and might be willing to take the time. Any other name would be a massive shock.