I feel like the Raen have likely been in Terncliff awhile. The Age of Blood, in particular, seems like a good catalyst for a Raen exodus into other parts of Hydaelyn. I use that as the time when my character's ancestors migrated to Ilsabard at least. Through the years they eventually integrate into the culture there which is also why my name doesn't follow typical Raen naming conventions.

I'd like some more concrete info in Lorebook 3 if it happens, but there's enough to work with just having a Raen hub outside of Sui-no-sato to make a decent background.