Where does this come from? I would like to read or hear it.
Honestly, i don't know. I've read so extensively... This is an obscure position. Let me give it to you as best as I can piece it together.
To begin with, it is believed that the church at Rome was founded by believers who first heard the gospel in Jerusalem at Pentecost, listening to Peter preach after he was filled with the Holy Spirit.
There is a famous document where a historian during Claudius' reign named Suetonius writes,
“Since the Jews constantly made disturbances at the instigation of Chrestus, he expelled them from Rome.”
There are two interpretations most probable for this. One is that there was a conflict between Jews and Christians in Rome, and the Jews got kicked out. The other possibility is that this uprising occurred during the time when Christians WERE mostly Jews, Messianic Jews, and they caused problems for the Romans, and so they got kicked out. This seems to be supported by Scripture.
Acts 18:2 “And he (Paul) found a certain Jew named Aquila, a native of Pontus, who had recently arrived from Italy with Priscilla his wife, on account of Claudius commanding all the Jews to leave Rome.”
So it would seem that the Church as it was originally founded in Rome was a Messianic Jewish Church, meaning full of Jewish believers.
It is believed that Peter had a hand in this for several reasons.
1. Acts 12:17 states that Peter "left for another place."
2. 1 Peter is written from "Babylon," first century Christian slang for the city of Rome, the heart of pagan hedonistic idolatry.
3. ECF referencing Peter in Rome. For example, Iranaeus, in "Against Heresies" states
“Peter and Paul were preaching at Rome, laying the foundations of the Church.”
The thing about Paul, is that by the time he wrote to the church at Rome, and by the time he actually got to Rome, a church already existed there.
After Claudius died, many of the Roman Jews that had been exiled did return, such as Aquila and Priscilla. But they would have found a very different church, with a Gentile majority and Gentile leadership. This was the Church that Paul wrote to.
It is thought that there was a LOT of ethnic tension in this Church -- in no other letter does Paul mention "Gentile" or "circumcision" as often. He seems to want to address the arrogance the church, looking down on unbelieving Jews as if they were better. But you have to wonder if some of the ethnic tension also existed between them and some of the minority Jewish believers. Was this the seeds of the eventual replacement of the Messianic Jewish Church by the Gentile Church? All this is speculative.
Anyhow, that's how I remember it, and I've tried to google the documents that I remember being connected to it. At my age, I just no longer remember every book I've read. I wish I could provide a better citation for you.