Lets assume that, somehow, Egypt’s Christians are able to take over the country by the 15th century. Yes, we’re going to spend most of our time on the ‘how’ of the matter, but I’m less interested in that.
What I’m interested in is how this impacts the overall affairs of Europe amd East Africa, and their interaction. Now, if we want to just go full-on EU4 map painting, we could posit a scenario in which Ethiopia manages to conquer Egypt, establishing a contiguous Christian Empire on the eastern coast of Africa. It would be fun. Also uneccesary for the discussion, as any situation on which Egypt is ruled by Christians works. We could also have the Mamluks lose Ain Jalut, and have the Mongols ally with the Copts, leaving them in power when the Mongols leave (if you’re open to a huge butterfly net).
How might the Europeans interact with the newly sovereign Egyptian Christians and their Christian African neighbors?