Justification by Faith: Metatheology for Metalutherans

Does anyone have any thoughts on the Pontificator's recent post(s) on justification by faith as a "hermeneutical rule" rather than a doctrine in the conventional sense?

The basic idea is that justification by faith is not so much concerned with the content of the Gospel, as with the type of discourse the Gospel is. The Gospel is promise-discourse, which makes unconditional declarations of a "Because ... therefore ..." nature, in contrast to the Law, with its conditional statements ("If ... then ...").

Fr Kimel quotes Robert Jenson as follows:

This dogma ["justification by faith alone, without works of law"] is not a particular proposed content of the church's proclamation, along with other contents. It is rather a metalinguistic stipulation of what kind of talking ... about whatever contents ... can properly be proclamation and word of the church ... It is this metalinguistic character of the proposed ... "justification by faith" dogma that makes it a doctrine by which the church stands or falls. If justification were a content-item of the gospel, along with other content-items, the question of which was most important would always be a matter of silly debate. But the doctrine is instead an attempt to state minimal identifying characteristics of the language-activity we call "gospel."

"In other words," writes Fr Kimel, "justification by faith is hermeneutical instruction to preachers to rightly divide law and gospel." He suggests that this "helps to explain why we hear so little about this rule for the first fifteen hundred years of the Church's history. People can speak a language well without knowing all the grammatical rules that govern that language."

I'm very suspicious indeed of attempts by ecumenists to use this sort of concept as a sort of magic wand for "waving away" the divisions between Rome and Wittenberg on the subject of justification (eg the Joint Declaration). But setting to one side the use of this concept in "ecumenical politics", what do people think of this "metatheological" perspective itself?

(It strikes me that there is a link here with Josh's recent posts on the various Reformation and post-Reformation confessions - particularly the direct, personal language of the Small Catechism and the Heidelberg Catechism, which is very consistent with the Gospel as promise-discourse, as contrasted with the flat, propositional, impersonal nature of the Shorter Catechism and other Westminster documents).