Like 
and 
, our resident Ionians-turned-Demacians (unless that's been retconed)?
All the other Demacian champions have updated bios and a short story...except for Sona and Xin Zhao.
Rito please.
[zombie-nunu-tears]
They're not getting any this update.
Basically Sona and Xin need more exploration beyond Demacia to truly flesh out their backstories, and they wanted to focus squarely on the folks who are grounded solely in Demacia.
and 
all Demacians will get their lore updated eventually
They pretty much explain it all here https://www.youtube.com/watch?v=pxjiCFo0NZM
