I suppose what is needed might depend on the setting itself.
Personally, I wouldn't actually mind if we have an scenario that doesn't involve time travel, or dimensional travel, or something
I agree. Chrono Cross was confined to a small archipelago and the setting was great. Same with Radical Dreamers, as you stated.
I feel like there are multiple story options we could take...
1.) The events of Chronopolis and the Time Crash, including the Polis War, as seen from those present.
2.) Some new city from the Future cut off from time and space with a mystery to solve.
3.) A giant ship in the far future with various biomes (think Metroid Fusion's space station), thousands of individuals in cryo suspension. Things go awry, people start awakening and the our party wakes up long after some other have awoken -- by the time the party wakes up, the factions have formed. Mystery ensues.
4.) Events in the fall of Guardia as seen by those present.
And that's just off the top of my head.