So at the end of Divergence Bren thinks that at the west coast is where the atevi wold stops, there’s nowhere left for the Shadow Guild to run.  Past the west coast is only Mospheira.

Well.

Right back to the first book:  an old man in a rowboat could reach Mospheira according to Banichi

Many clues sprinkled through the whole series of books about smuggling and most recently a special mention of the sale of illegal atevi antiquities frrom the Southern Isle and the market for atevi artifacts on Mospheira. 

Hmmm, Asgard Corp involvement maybe. 

And also right back to the third book: Hanks and Direiso each thinking they can use the other and get the better of the them.  So now two organized criminal groups:  the atevi Shadow Guild and the human “Mospheiran mafia” each thinking they understand the other and can take advantage of them.  But everything in the whole series tells us that neither side really understands the other and neither side truly comprehends the intentions of the other.

Not to mention humans landing on the Mainland and havinng to be sent on to Mospheira. Even if it's not happening yet preparations are surely being made for it.

With Homura and Momichi in the middle of it.