Well by the time of the Crusades Ethiopia was neck-deep in its Dark Ages with most of Ethiopia under the Zagwe dynasty except for Shewa, which was held by the Solomonic dynasty. Negus Yemrehana Krestos is best known for the construction of a large church on Mount Abuna Yosef, and his successor, Kedus Harbe, tried to break the Ethiopian church away from Patriarch of Alexandria by appointed his own bishops, but the prelate refused, so Harbe wrote to Al-Aziz Uthman requesting for his permission. Uthman was apparently approving of such a move at first, until he realized that with so many of their own bishops the Ethiopians could elect their own Archbishop and be completely free of Egyptian influence, and might develop "enmity and hostility" toward their Muslim neighbors, so the deal was nixed.
ITTL the Crusader kingdom of Egypt might approve of such a move, or at least work out some sort of deal increasing ties between the two, which would legitimize the Zagwe dynasty by the establishment of its own Ethiopian Church, and might pull the kingdom out of its Dark Age some hundred years or so before IOTL.