From what they've revealed so far, story mode being character-based means it'll be something a bit closer to how DW5 did it, where you follow the character's career (as defined largely by the book) and you play through battles/events that they participated in. So in that way, someone like Sun Ce is going to have stories told through the early portion of the era, while scenarios for Sima Zhao would start much later.
They said there won't be any "What If's" to be told this time around, but it remains to be seen how they'll handle characters like Sun Jian or Dian Wei (let alone someone like Zhang Jiao), since their careers aren't that long. Then there's others like Lu Lingqi (confirmed to have a story
here), for which no much is known, and they'd have to wing it anyway.