Maybe Your suggestion will need a high level of modding.
I'm interesting your idea. But it seems to be a hard way.

Because This mod is simple
Mechanism : Make new property tile -> give civ property to tile ->give tile to wonder

It is can be just new table in .sql

But your idea need "if player capture someone's capital"
-> Delete civ property of that civ
-> Give civ property to player
+ not only player but also Ai each other.

It maybe need .lua file and functioning.

I would suggest making wonders culturally specific, like giving both rome and byzantium access to the coliseum and hagia sofia, or giving stonehenge to england, scotland, and gaul. This way you still have to compete for wonders and they won't look out of place when you find them.