They will be a chapter or arc that focuses on students from million of years in the future.
The story already includes a few prehistoric animals such as Tyrannosaurus Rex, Neanderthals, and Mammoths, and there was an arc of Tyranno-sensei's high-school days which took place during the K-T Extinction. While Bungo Yamashita's preference on the subject is unknown, speculative evolution works such as After Man: A Zoology of the Future and The Future is Wild are popular in Japan. The arc could include future species designed by the author. As a bonus, a teacher from this era could be one of the main characters, such as Ranka.- Jossed.
About peaceful predators and humans
Every time we see any predator animal in the series, they are at best harmless and/or friendly and at worst won't do much (even the bears in the past didn't cause much harm when they definitely should, implying they held back). Given that change of behavior despite the fact that these predator animals still need meat for their meals, the likely solution is that there's no need to hunt anymore because there's enough meat for everyone. Now combine that with the near extinction of humans..a human farm for food resources doesn't seem too far-fetched, especially given that we are doing the same thing with animals.