It cannot be.
First off, the promises to Israel by God...the covenant...is not even in dispute. That's what a lot of people who use the false term of "Replacement Theology" don't seem to get. The actual dispute is what Israel is. What is Israel? How do we know who are God's People?
We know this because we become them by adoption. All, men and women, Jew or Gentile, become an adopted son of God by their baptism, for in it we are baptized in Christ's death, burial and descent, and resurrection.
Are Jews who are not adherents of Christ saved? No. The NT makes that very clear. But what of the Remnant? That's very easy: they are the Jews who did not abandon God and accepted Him Incarnate as Lord and Savior. All the others have rejected His salvation and will be Judged accordingly if it is His Will.
In both Judaism and Christianity, there has always been the importance of "ancientness" and "history". Judaism is all about the history of a nation and its relation with God; Christianity is no different, except its nation is all nations...all people in Christ. One nation of nations, if one wants to put it this way; a God that shows no partiality and is a respecter of no one. Without a historical link, the country of Israel cannot be the successor, and it cannot even be a spiritual one because of what happened in both the Gospels and in proven history: in the Gospels, the temple was broken, telling us the end of Judaism as of any merit. That was further enforced by its destruction a few decades later. Judaism is a dead religion, but God did not forsake anyone, for in Christ's blood is a new and final covenant; a continuation of salvation's history and with His relationship with His people. This time, however, it is with everyone, for God did not incarnate solely for Jews but, being human...just being incarnate...becoming part of creation by taking creation unto Himself...He includes now all peoples...all things into His saving embrace.
But this is all in Christ. What is the Mystical Body of Christ? The Church; the community in which we are initiated into by baptism. The Church isn't the replacement but the continuation of the True Israel; the Covenants, which Jesus condensed and summarized in how they should have all been followed in His Two Great Commandments, are still there. The only things gone are the old theologies no longer necessary because of Him and His Sacrifice: no more ritual/holiness laws...no more ritual purity...no more social laws. He was the Torah and nailed it. In Him we find our salvation, and our entering into Him is our accepting of this continued covenant and membership with Abraham and all our spiritual forefathers.
This is Christianity. All else is not.
