There are but two survivals of the explicitly Jewish conception of the coming kingdom in the Gospels, without any thought of inclusion of Gentiles, in Matthew 19 and Luke 22.
But the choice of twelve disciples by Jesus as a function of this explicitly Jewish conception of the imminently coming kingdom as a kingdom of the twelve tribes of Israel is also evidence. If the former nearly was expunged from the record, the tradition of the twelve survived because they did.
Those elements, the future Jewish kingdom and its twelve Jewish judges, are consistent with other surviving evidence of Jesus' original Jewish Gospel, for example with the charge in Matthew 10 and 15 not to go into the way of the Gentiles but to go only to the lost sheep of the house of Israel, as well as with the scattered derogatory references to Gentiles, for example as dogs.
Needless to say, a future Gentile kingdom would have required more judges than the twelve, and a Gospel to the Gentiles worked out to go with it. The latter was the innovation of Paul, not coincidentally a missionary Pharisee. The former never existed but for him.
And Jesus said unto them, Verily I say unto you, That ye which have followed me, in the regeneration when the Son of man shall sit in the throne of his glory, ye also shall sit upon twelve thrones, judging the twelve tribes of Israel. And every one that hath forsaken houses, or brethren, or sisters, or father, or mother, or wife, or children, or lands, for my name's sake, shall receive an hundredfold, and shall inherit everlasting life.
-- Matthew 19:28f.
Ye are they which have continued with me in my temptations. And I appoint unto you a kingdom, as my Father hath appointed unto me; That ye may eat and drink at my table in my kingdom, and sit on thrones judging the twelve tribes of Israel.
-- Luke 22:28ff.
That this conception of a future Jewish kingdom was there from the beginning explains the many instances of the disciples' fascination with who would be greatest in that kingdom which survive.
Those discourses need not be historical in all their particulars. The failure of the Jewish kingdom to appear necessitated rationalization of the conception involved under and for the new circumstances. Hence the emphasis upon selfless servanthood in the light of the reinterpretation of Jesus' death as a sacrifice for the sins of the whole world.
At the same time came the disciples unto Jesus, saying, Who is the greatest in the kingdom of heaven?
-- Matthew 18:1
But he that is greatest among you shall be your servant.
-- Matthew 23:11
And he came to Capernaum: and being in the house he asked them, What was it that ye disputed among yourselves by the way? But they held their peace: for by the way they had disputed among themselves, who should be the greatest.
-- Mark 9:33f.
Then there arose a reasoning among them, which of them should be greatest.
-- Luke 9:46
Luke says the dispute among the twelve persisted even to the Last Supper, which is remarkably self-absorbed of them given the supposed gravity of the moment. It also suggests the lectures by Jesus all along didn't do them much good. It's almost as if the fact of the incipient nativism were a pretext for Luke's narrative invention. And then there's the irony that even in correcting the disciples' preoccupation with themselves, Luke still makes Jesus contrast the proper behavior with the improper behavior in terms of Jew vs. Gentile.
And there was also a strife among them, which of them should be accounted the greatest. And he said unto them, The kings of the Gentiles exercise lordship over them; and they that exercise authority upon them are called benefactors. But ye shall not be so: but he that is greatest among you, let him be as the younger; and he that is chief, as he that doth serve. For whether is greater, he that sitteth at meat, or he that serveth? is not he that sitteth at meat? but I am among you as he that serveth.
-- Luke 22:24ff.
But ye shall not be so.
It is easier to explain the more inclusive conception of the kingdom of God with Gentiles as a development from this original narrower one without Gentiles than the other way around.
The narrower conception died hard, especially for example in the person of Peter, whom Paul accused of lingering hypocrisy about it in Galatians 2.
Luke, on the other hand, paints Peter in a more sympathetic light, in Acts 10, 11, and 15, showing how God himself miraculously intervened to change Peter's opinion about Gentiles.
But that Peter persisted in the nativism so long is the point. He didn't invent it. He got it from someone and stuck with it the whole time almost up until the moment he disappears from Luke's narrative never to be heard from again.
