Of course, it is possible for many different types of evolution to happen in any given state. We can imagine many different outcomes for any state. For example, these states might have become insular and xenophobic like Tokugawa Japan was. They might have become Islamic theocracies. They might have melded themselves into one large state that would have covered all of East Africa. Any of this is possible. Let us look at the last two of these examples since they are, in my view, the more plausible possibilities.
In today’s world, we see Islamist groups trying to set up states that will be dominated by religious leaders. These might look something like Iran, whose highest authority is a religious leader, not a secular one. Could this have happened in the states of East Africa? It seems like it would have been possible. These states were clearly dominated by Muslims and yet were exposed to people of other faiths. It seems likely that the Muslims could have chosen to adopt a defensive posture against these other people. They could have based their states’ identity on their religion and they could have rejected all other people. This would have led to a situation in which they would have cut themselves off from trade with non-Muslims.
Another possibility is that the city states of East Africa could have merged. This is the more interesting possibility because it might have changed the course of history. If the East African states had merged, they might have created a large state with many resources. They might have merged because they all spoke Swahili and all had similar trading interests. If they had done so, they might have become very powerful. They might have been able to resist European colonization successfully. There might have been a strong East African state that would have remained independent and would have continued to be a power in the world.
These are both possible ways in which these states could have evolved, but it is not clear if either of these would have been very likely.