I don't know what "Replacement theology" means. There was a clear transition of priesthood and covenant. For those Jews that followed Jesus, witnessed the crucifixion and remained Christian, those are the bearers of the true Judaism. Every other Jew that walked away from Christ is an apostate. It isn't a replacement. They walked away from God in favour of the teachings of their elders (a brood of vipers, as Jesus said). These same may be saved by grace, but were cut from the tree.
Some natural branches are cut off and other branches are grafted in. At the end of the grafting process, some of the natural branches are grafted back in (not all, because not all of Israel are Israel). All whom are intended for the tree will become part. It is important to note that these "natural" branches are referring to branches that were considered natural prior to the crucifixion, and includes earlier converts to Judaism and other forms of Israel. These earlier converts would have been grafted-in in the same manner and are considered part of the natural tree by Paul within Romans 11.
"Thou wilt say then, The branches were broken off, that I might be grafted in. Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear: For if God spared not the natural branches, take heed lest he also spare not thee." - Romans 11:19-21 KJV
If we look back at Jeremiah:
"Be thou instructed, O Jerusalem, lest my soul depart from thee; lest I make thee desolate, a land not inhabited. Thus saith the Lord of hosts, They shall throughly glean the remnant of Israel as a vine: turn back thine hand as a grapegatherer into the baskets. To whom shall I speak, and give warning, that they may hear? behold, their ear is uncircumcised, and they cannot hearken: behold, the word of the Lord is unto them a reproach; they have no delight in it." - Jeremiah 6:8-10 KJV
The word of the Lord is Jesus Christ:
"And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth. John bare witness of him, and cried, saying, This was he of whom I spake, He that cometh after me is preferred before me: for he was before me. And of his fulness have all we received, and grace for grace. For the law was given by Moses, but grace and truth came by Jesus Christ." John 1:14-17 KJV
Not all of Israel is saved. Only those that are in Christ:
"Abide in me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me. I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing. If a man abide not in me, he is cast forth as a branch, and is withered; and men gather them, and cast them into the fire, and they are burned. If ye abide in me, and my words abide in you, ye shall ask what ye will, and it shall be done unto you."
" - John 15:3-7 KJV
The inheritors of the promise are those in Christ:
"Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel: Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed." - Romans 9:6-8 KJV
"Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ." - Galatians 3:15-17 KJV
Romans 3:24-26 covers the topic of remission of sins prior to the crucifixion:
"Being justified freely by his grace through the redemption that is in Christ Jesus: Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God; To declare, I say, at this time his righteousness: that he might be just, and the justifier of him which believeth in Jesus." - Romans 3:24-26 KJV
The topic becomes blurry when we consider that Jewish Christians eventually just called themselves Christians. The hatred for Jewish Christians by some Orthodox Jews is real and heaven forbid anyone denies it. Calling Christianity a "replacement" is hateful to those founding Jewish Christians and their descendants that believe in the fulfilment of prophesy by the coming of Christ.
We should not look at the current political state of Israel as having any necessary bearing on the Biblical nation and people of Israel anymore than places like Jerusalem, New York, having any necessary bearing on the Biblical Jerusalem: "(But he shall have one tribe for my servant David's sake, and for Jerusalem's sake, the city which I have chosen out of all the tribes of Israel: )" - 1 Kings 11:32 KJV
Make your case.