Well, granted the main focus of power will be more toward Mombasa or Kilwa, but still. Come one, come all to see a tale of a Persian Merchant making way from Persia to East Africa due to a dispute at home leads to his semi-exile. Here on the Zanj Coast he makes a second home, even founds a city on Mombasa or Zanzibar around 540. His fortunes grows slowly once more as he forges trade between Zanzibar, Arabia, Persia, and India. Time continues to flow and so does his family as he passes away his son takes up the mantle of a strong merchant empire with strong connections across the Zanj Coast and across the Indian Ocean. All this time the interaction of man leads to those who dwell along the coast to take up the Faith of Fire. Time goes on further and upon the Call of Submission to Allah is heard in Arabia! Soon spreading to the four winds as the Caliphate even conquers ancient Persia. Muchly angry at this the descendents of the Persian Merchant give safe haven to Pagan Arabs and Persians who find safe haven and new opportunity along the Zanj Coast. These refugees settle along the coast forming new cities and melding into what would have been the Swahili Culture, but now is something new and different.
The descendents of the Persian Merchant encourage the spread of civilization throughout the coastline of Africa. Will they be able to stand the test of time against not only Muslim, but also upstart European?