I think that Thingol and Melians new kingdom in Valinor and Greenwood 2.0 once Thranduil gets there would be VERY close kingdoms. Even geographically, I think, they would be close compared to other elven Kingdoms. Only two or maybe three days of travel between them. A constant stream of elves flutter back and forth between the kingdoms and the incredibly well worn path between them comes to be known as: The Road to Friendship.
The name started out as a joke, and it was used ironically at first but like most things that are used ironically somewhere along the way it stopped being ironic.
Their economies and cultures end up being so intertwined Noldor elves often have trouble distinguishing whose Sindar and whose Silvan.
So I know that Oropher had the crown first, but I honestly don't see Thranduil (or the Silvan elves) being willing for him to take it up again once they reach Aman. Thranduil led and ruled them through unimaginable horrors for centuries and never once gave up or stopped giving his people the support and love they needed. And the Silvan elves return the dedication and love back to Thranduil tenfold.
The thought of Thranduil giving the crown away had literally never occurred to anyone. Even then, if he didnt want it, I think the Silvan elves would probably elect Legolas instead and not Oropher again.
Which is fine with him, Oropher would never expect Thranduil to do such a thing, and gracefully steps down next to Legolas and slaps the title 'Prince' across his head.
But, like Legolas, it is not just the Prince of Greenwood 2.0 but also Prince of Doraith 2.0. Oropher and his wife live with Thingol but often go to visit Thranduil and his family. Meanwhile, Legolas lives with Thranduil but frequently travels to Thingols realm (along with several others and pretty much anywhere else that takes his fancy. Such as Elronds and Celebrians new home and his occasional invitations to Yavanas Gardens or Aulë's forges).