Makes a lot of sense.That video sounds interesting but that doesn't sound right. Because southern Sudan during that period was doubtfully that Christian-heavy (I would imagine that it was a mix of traditional religions and Christianity) and in any case Georgia and Armenia were likely far more Christian-heavy than southern Sudan (and far more organized). If they could be vassalized, I see no reason why the Ottomans would not want to retain southern Sudan, which at the outbreak of the war was already technically Ottoman since it was a part of Egypt and Egypt was de jure a part of the Ottoman realm. They might leave the south to its own devices, but still retain control over it since it was technically already theirs and because it enabled control over some of the sources of Nile and of a greater stretch of the Nile system (which is vital to Egypt).
Of course, all of this is assuming that the already declining empire could sustain control over all this land.