I waded into a discussion about this at the HoB/D listserve earlier in the evening, after re-reading John 14 and the verses that come just before it.
In principle, context really matters in this case, even if we sidestep debate about what the "historical Jesus" said or didn't say, and confine ourselves fairly narrowly to the internal integrity of the Fourth Gospel.
I am puzzled that conversations around John 14:6 often do not reflect more often that the verse is a direct response to Thomas's very pressing and somewhat personal question: "How can we know the Way?" The passion of the question seems to stem from an understandably fearful reaction to the foretelling of Peter's denial and Jesus' imminent death and departure.
Taken in the broader context of John, this seems to be Christ speaking lovingly to the Johannine community of believers as they wrestle with doubts and their identity in a time of conflict. And, as so many have written (Bill Countryman's The Mystical Way in the Fourth Gospel is but one wonderful example), it is a statement more broadly given for Christians undergoing conversion, struggling with a journey of deepening faith -- a pilgrimage even -- through the sacramental life, moving into the tensions of a deeply personal and, at the same time, communal relationship with God in Christ.
To therefore use 14:6 in isolation as a litmus test for the orthodoxy of "believers" or an exclusive, narrow theological statement about how God's salvation works (through the Church only?), strikes me as bringing violence into an inspired text -- a passage, chapter 14, that seems intended to be more pastoral than polemical, and to bring comfort to a community of disciples in distress.
After all, it opens with these words, "Do not let your hearts be troubled. . ." (14:1)
At the end of the day, John 14:6 comes alongside words that are fundamentally meant to edify the Christian community, to draw us into the holy mystery of Christ speaking through the gathering of the baptized around the eucharist, and to bring us along further together in the journey of discipleship.
Yes, it says Christ is central for us as Christians in our knowing God. But anything more universalizing or triumphalist than that may be presuming too much, and brings meaning to the text that I'm not sure is intended.