I cannot stress enough how much I think the general approach taken by Goodacre and DeConick needs to be appreciated and incorporated into our own thinking about Jesus within the church. Neither scholar is necessarily saying that we can't really know about Jesus (to be sure, there are some who say this), but both caution us to remember that what we do know and what we think we know are only parts of the picture. There are so many things about Jesus we cannot know, ranging from minor details (what did he prefer to eat, did he have a lisp, and so on) to more important information (what provoked him to "go public," how did his understanding of God develop, and so on).
What's worse, the things the gospels do tell us about Jesus are often affected by the things we don't know, which adds an element of contingency to all of our talk about Jesus. Goodacre, in fact, uses the slightly different but related image of a puzzle to ask, What if key pieces are missing? As Goodacre has sensed, this is an important question that may have catastrophic consequences on all of our scholarship. In my own work I have asked exactly the same question with respect to understanding the gospels, suggesting that our knowledge of how the texts "worked" in their first-century contexts is hugely hampered by our inability to observe them at work. That is, for all the talk about the many written sources about Jesus potentially floating around in the earliest centuries of Christianity (for example, in The DaVinci Code, or even in Luke 1.1–4!), we simply don't have any access whatsoever to the way normal Christians spoke about Jesus and the way our textual remains related to that way of speaking. And I can't help but suspect that this is a "key piece" indeed.
But for those of us more accustomed to accepting the canonical gospels for their testimony about Jesus, the question of missing pieces can be reframed slightly. There are indeed many things we would like to know about Jesus, things about which the gospels are simply silent. But the gospel writers did convey what they considered were the key pieces. For many people this simply won't be good enough, and I can certainly understand and sympathize with this. But for those people who hold to some view of the texts as "inspired" (however we understand that term), the biblical portrayal(s) of Jesus will, in the end, be sufficient. But I think I'll stop now before I begin to channel the shade of Martin Kähler!