As far as I'm aware, historically, the Swahili Coast trade from the geographic areas of the Middle East, Persia and West India terminated with the furthest point south, on the eastern African coast, at the Kingdom of Kilwa (in modern day Tanzania). Due to the winds and currents to make the journey back north.
It wasn't until European exploration (Portuguese) along the coast south of Kilwa that further trade opened, and European colony markets were created. Portuguese East Africa, obviously, had Inhambane as a settlement and coastal trade market (this, in game, is a Rozwi possession). I don't know if there was further, southern Portuguese outposts along the coast south of modern day Mozambique - Vasco de Gama named the land, now part of the RSA, as Natal (well, Natividad, etc., due to the time period of discovery, if memory serves me correct), but Portugal didn't settle south of Maputo, as far as I'm aware (Maputo would be in Rozwi lands, in game, but isn't shown on any maps, nor mentioned as a Rozwi asset). Could be wrong.
By 1700, I'm not certain what amount of coastal trade to these Portuguese markets was non-European. Not that it really matters, I suppose, as this is a game and not historically set in stone. In our game world Africa's east coast trade will be open to all nations that can sail south along the continent's coast, no doubt. So Persian and Indian middlemen traders will be available to open a 'silk road' link for the Far East's rice trade.
I keep falling into the trap of thinking that my Rozwi is a tribal group of cattle farming plainsmen in Zimbabwe. Where as, with the fact we've coastal possessions and Inhambane, Rozwi's technology and abilities will be more akin to such as the (historic) coastal Kingdom of Kilwa than I think.
Thanks for the information and help, Stuart and Kerensky
(Kilwa was actually the Kilwa Sultanate, and Muslim)
https://en.wikipedia.org/wiki/Kilwa_Sultanatehttps://en.wikipedia.org/wiki/Kilwa_Kisiwani