There was in interview with Kelly Kahl (CBS scheduler) a few days ago where they asked about the state of CBS reality programming and how they're adding 2 new ones this year. He basically said they have stable performers right now which allows them to experiment with these new shows to try to find the next generation of reality shows for the network.
So they are certainly looking for new reality shows as long-term replacements, but they still have to air and perform well to show signs of longevity. Remember how they thought Hunted was going to be their next big hit as well. We should hopefully have a few more seasons of TAR in us (obviously at least 2), so let's just enjoy it while it lasts.
I've been thinking about the longevity of their "big 3". One of the things that got people interested in this lineup was because those shows
were a new kind of programming at the turn of the century. Survivor: Borneo and Big Brother 1 were HEAVILY covered in media when it first premiered to a similar status of pro sports. TAR came more or less than a year later, but still within the same attention span to catch onto people. Following CBS up to this incoming two-decade milestone, the floodgates for these strategic and skill competition shows have widely opened as a cost-effective form of entertainment for cable and other channels (American Idol, American Ninja Warrior, The Challenge, RuPaul's Drag Race, Project Runway, etc.), being one of many factors as to why the general audience who did use to watch the originals no longer do.
I think there is still more concepts that can be uncovered and be relatable for general broadcast. It just needs to be gimmicky enough to create a hook for people, but also strong enough to make unique twists and turns for the show along the way to keep the audience. First "concept" I can hint at is that the escape room trend is going nowhere and getting more elaborate as time goes on. Perfect opportunity to add in over-the-top TV flare with this newer kind of game and get people with different interests, goals and lifestyles engaged and auditioning.