Hagner on Paul, early catholicism in the NT, and a "Canon within the Canon"

If you are like me, you are excited to see the release of Donald Hagner’s New Testament: A Historical and Theological Introduction (Baker, 2012, coming in November). While it is not officially “out” yet, I found the snippets on Amazon “Look Inside” tantalizing. I was particularly interested in how Hagner places Colossians under his chapter on Paul (“Paul and His Epistles”), but Ephesians is put in a separate chapter with the deuotero-pauline material and considered a form of “incipient early catholicism.” Despite this separation of Ephesians and the PE away from Paul himself, Hagner denies the kind of dichotomy set up by Kaesemann. Instead, Hagner argues,

We may well be persuaded that Paul’s articulation of the gospel is the clearest and most compelling, and that, in this limited sense, Paul serves as a canon within a canon. But there is a reason for the emphases of the later books of the NT. The tendencies of incipient early catholicism have as their purpose the preservation and protection of the gospel from corruption. Incipient early catholicism is not to be set over against the gospel. Rather than a denial of the gospel, the tendencies of incipient early catholicism exist for the sake of the gospel and the church” (p. 613)

What do you think? Does or should the genuine Pauline letters serve (even in some sense) as a “canon within a canon”?