Re: A Song of Ice and Fire books
The most hilarious option: have Dunk and Egg go there for some godawful reason. At the end of the story they go, "Let's never speak of this again. If anyone asks we were hanging out in Dorne the entire time."
But anyway, I don't think we're going to visit Sothyros in the main books. I'm not even sure we're going to manage to get to Asshai despite Quaithe basically spelling out to Dany she is going to go there at some point before the end (or at least she has to go "beneath the shadow"). That's the only reason I think we have to at least get to Asshai/Far East. If it weren't for that one particular line I'd say he simply doesn't have time.
Thus far nothing about inland Sothyros in any prophecies, so I think he will ignore it.
Besides I think he has mentioned that Sothyros is kind of an homage for the Africa-region in Conan, which was mostly unexplored and mysterious as well, with Conan having a few adventures on the coasts but that's about it. So Victarion being on the northern coast of it might be the extent of it.