If there is a chronomancer new setting, this would need a lot of time to create the background and the metaplot, but there is a lot of possibilities. For example fight among worlds like the manga "Bokurano" or the event "Time Runs Out" by Marvel Comics, or something like the Battleword from the last secret wars saga. A demiplane could be a mixture of Dark Sun and the mini-setting Jakandor and Council of Wyrns, or a demiplane when Raitlin is the god who destroyed Krynn and prison in his own post-apocalypse version of Ravenloft. The setting "Dragon Fist" would be the Oriental continent from Greyhawk's world. Why not the return of the time dragons and the le-Shays, the fays from "Epic Levels Handbook"? Let's imagine a FR without the spellplague, or Dragonlance without the 5th age, or the aliens from d20 Future invading the world of Dark Sun. Or a time sphere what is a mixture of Kaladesh (from Magic: the Gathering), Transformers and Iron lords of Jupiter (from Dungeon Magazine #101). Other time sphere could be "guest artist" by other companies, for example mixing D&D, Legend of Five Rings and 7th Sea.