Regardless of whether PA was oral or written, GJohn's absorption of PA demonstrates that, into the second and third centuries, written gospel texts, even authoritative ones, functioned in a 'performance mode' in light of the texts' scribe (or performer) and readers (or [intended] audience). The interpolator was both a reader of GJohn's author and an author in his own right, modifying GJohn in light of his (intended) audience. PA is thus primary evidence that long-held assumptions that written tradition was 'fixed' while oral tradition was 'free' are incorrect. (Keith 2009: 259)
Keith's point about the problematic assumptions upon which NT scholarship has depended since at least the rise of form criticism in the first third of the twentieth century is dead right. If we accept any literary explanation of the synoptic gospels' interrelationships (e.g., the Two-Source Hypothesis or the Farrer Theory), we are similarly hard-pressed to explain how later evangelists could handle the text(s) at their disposal without a sense that they were falsifying those texts. The answer (or a significant part thereof) must be the altogether different conception of fixity current among ancient Christians. Moreover, this conception of fixity (for the early Christians clearly and demonstrably did think their traditions were fixed and stable, despite [and even in the face of] the variations between them) applied to both oral and written expressions of tradition and was capable of, among other things, incorporating interpolations such as PA.
But that's not actually what caught my interest, and so I've emended this post's title by adding the parenthetical qualifier. I was particularly pleased to see Keith's suggestion that the [written] text of John's gospel functioned along the lines of a performance of the Jesus tradition. This idea has not, unless I've missed it, played a significant role in his argument throughout The Pericope Adulterae; it is, on the other hand, a significant aspect of my argument in Structuring Early Christian Memory: Jesus in Tradition, Performance, and Text (London and New York: T&T Clark, 2010). The idea of the written texts themselves—texts that have been subjected to intense examination in all their minutiae and presumed to exist in a stable form similar to our familiar NA27 or UBS4rev—as performances of the tradition rather than the final expressions of the tradition will likely be one of the (if not the) most significant advances in gospels scholarship in the next generation. But then again, I would say that, wouldn't I?