I sure don’t intend to speak for Andrew, but I believe you might be making his comments prove too much. In fact, over lunch today, I was reading toward the end of Re: Mission where he talks about inclusion of the Gentiles in the new people of God and how that fits into the story including its brief anticipation in prophecy.
I believe (and I could be wrong) what Andrew is arguing is not that the Gentiles were never inteded to be included in God’s new covenant people, but rather that inclusion was not something that part of Jesus’ evangelical mission or part of the gospel as it was present at his time. The keystone that makes Gentile inclusion possible is the Law no longer serving as the definition of covenant faithfulness, and this wall is torn down in the death and resurrection of Jesus. In other words, it is a phenomenon that Paul and the apostles are witnessing and active participants in, but in terms of Jesus and the OT prophets, it’s a faint, fringe issue.
Obviously, you disagree on how faint it was, especially with Jesus, and I’m finding that debate between you two interesting, but I don’t think Andrew is saying that the Gentiles were never meant to be included in God’s people.