Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
My brother, read the Kebre Negast in its own context. What was Adam from Creation? A true born King. So the line we read of this Ethiopian meta-narrative is the line of the Kingship established by God through Adam, descending in these patriarchs till Abraham and Isaac and Jacob and then Judah. Now here is where it gets interesting.
Yes, the primary thesis of the Kebre Negast, the Honor of Kings, is to suggest the theocratic origins of kingship, particularly of the Adamic/Davidic kingship which not just Ethiopians, but princely and kingly dynasties across Europe, Asia and Africa have claimed or asserted for centuries of time. Even for those who did not pretend to have Davidic ancestry, still Davidic symbolism and imagery permeated these Christian sovereigns from France and Germany across through Byzantium and Russia. More specifically though, it explains that the very purpose of Adam's genealogy was inevitably our Lady the Virgin and our Savior Jesus Christ who took His Flesh from Her and Her family. So really, when we read the Kebra Negast (or even the Old Testament) I explain to my Sunday school classes that we are reading the family history, the genealogy, of Jesus Christ. All these characters are the people whose lives culminated with the birth of Our Savior. Their daily lives build together over thousands of years to perpetuate a single family within the midst of all the peoples of the world, that the Savior of all these peoples might be born into that family line. But there is a contradiction, God promised that this line would continue on in perpetuity on the earth, and yet also acknowledged that this line should culminate with a Virgin Birth of a celibate God-man? How can the line continue if it ends with God?
Simple, it didn't end, as the Kebra Negast explains, it branched off. The line in Jerusalem was preserved that Jesus Christ would be born there to fulfill the entire purpose of all our existences, namely the Incarnation and the Crucifixion and the Resurrection of the God-Man, whose flesh came directly from Adam. So when we read the Old Testament, we are reading that God maintained the Israelite society there in Jerusalem, even after exile and return, that the Christ might have an earthly family and earthly society to originate and be born into.
The Ethiopian branch of the Solomonic line was the maintain an earthly perpetuity of the Davidic Covenant within the Emperors and societies of Ethiopia. When you generally ask other Christians how to explain the Davidic covenant, they explain that it is fullfilled in Jesus Christ, but this simply does not make sense in the context of several verses of the Old Testament. Rather, the Davidic Covenant is fulfilled within the context of the line of Solomonic Ethiopian Emperors, unbroken in succession from David and Solomon until this time, still represented in the Imperial House of Sahle Selassie and the princes of HIM line, including the Crown Prince HIH Zere Yacob who is recognized by the Ethiopian Orthodox Tewahedo Church, and also the prominent HIH Prince Ermias, a leading activists with potent political ambitions.
In reality, this past 40 years without a monarchy in Ethiopia has been a temporary phase, and to say the Davidic covenant in Ethiopia has been made null and void because of the current circumstances would be as silly as to say that the Alexandrian Church lost its legitimacy with the long exile of Saint Athanasius. In Ethiopian history, there have been several similar incidents, and while this has been the longest gap, it is by no means the only. So I would say it is faithful to assume that in some capacity the Ethiopian Monarchy, according to the Davidic Covenant, should rightfully return to Ethiopia. There are dozens of monarchies in the world today, and if anything, Ethiopia in this era of ethnic federalism could benefit greatly from Ethiopia's traditional source of Pan-unity in the person of the Emperors. Their tangible power has ALWAYS been limited, it is their spiritual and symbolic power that has shaken the core of Ethiopianness across time. Even today, look at the rise of Haile Selassie paraphernalia thanks to the popularity of Rastafari rejuvenation of Imperialism, kids where as many Haile Selassie t-shirts as Rasta folk! We're becoming indistinguishable even!
So the Davidic Covenant is there to say to the world, God is true, the Bible is true, the Apostolic Church is True. The Emperors have been the Defenders of the Orthodox Faith and the temporal heads of the Church, and they serve as almost living saints in Ethiopian Orthodox theology. God cooperates with the Emperors and the Church in a Divine balance which the democratic governments tried with the separation of powers. The Emperors are crowned by the Church, and the Church is maintained and supported in the Grace of God through the hands of the Emperors. It is a mutual structure of support, like two sides of a vault arch.