The Challenge is currently on a hiatus, but it’ll be back soon. We have three seasons coming down the pipeline: All Stars 4, The Challenge: USA 2, and Season 39 (main series).
This means there’s a lot of people who could be on the show, but who belongs where?
All Stars

You’d think that originating on an MTV show would qualify you for the main series, but at this point, that’ll get a person cast for All Stars. Cast members who debuts on The Real World, Road Rules, and Fresh Meat are eligible for All Stars — even if they’re still active on the main series.
At this point, we’re also seeing Are You the One? bleed into All Stars, but at this point, I think we’d only see people who debuted prior to the international invasion on War of the Worlds. I wouldn’t be shocked if we saw Amanda, Nelson, Tori, or Hunter on All Stars in the future, assuming the show is renewed after season 4.
The Challenge: USA

Based on season 1, the criteria for getting on the show is quite obvious: The person started on a CBS show. Survivor, Big Brother, Amazing Race, and Love Island stars will be eligible to be cast on future seasons.
On season 2 and beyond, Challenge legends will also be invited to this show, especially the ones who originated on CBS. So, I’d expect people who have become staples of the show (think CT, Nany, Devin, or even Jay) to get invited on the future. But, I don’t think someone who originated on an international show will get the invitation. I could be wrong, and I could see someone like Kyle, Theo, or Turbo get cast because they’ve become Challenge “legends.”
Main Series

It’s obvious that production can’t simply cast people from Real World, Road Rules, and Are You the One? anymore because those shows aren’t really giving us new faces. So, they’re pulling in cast members from all over the world.
What qualifies someone to be on the main series? In terms of returning cast members, there’s an emphasis on recency. People who haven’t appeared on the three most recent seasons are very unlikely to come back unless they’re legends like Laurel or Bananas. But if you’ve done a prior season, you’re technically still on the roster as a main series potential.
The next question: What about the CBS cast members? Likely, production is going to look for people who have potential, but aren’t huge names for CBS. Someone like Tyson, Janelle (Big Brother), or Xavier are probably going to be included on The Challenge: USA before the main series. Someone like Olivia, Analyse, or Tommy demonstrated that they could provide entertaining TV, but they weren’t the main stars of their seasons.
Beyond the MTV and CBS stars, it’s seemingly random. International personalities are much more likely to get cast if they have some ties to foreign MTV networks or if they live in a country that will air MTV programs (for example, The Challenge aired in Germany once international stars started to compete).
But is any of this a perfect science? Of course not. Some people, like Wes, could do any of the three pillars in The Challenge world. Other people will be isolated to one. But as it stands now, it seems like the older Challengers are more likely to be seen on Paramount+ or CBS than MTV.
