In this Theology of the New Testament (which would be more accurately titled Theologies in the New Testament), Rudolf Bultmann mentions the evolution of Christ as title for Jesus to proper name. Jesus goes from being "ho Christos" (the Messiah, the Anointed One) for Jews to "Iesous Christos" for Gentiles. Later, in Latin-speaking Christendom, "Christos" is not translated, but transliterated into Christus, thus solidifying its status as proper name. The same, obviously, is true of the word's move into English. Christ denotes a person, not a title. Commenting on this Bultmann writes,
As a title, "the Christ" was not understandable to the Hellenistic world and any such paraphrase as "the King" (ho Basileus), which would have corresponded in content, was out of the question, in the first place because "King" ad no soteriological meaning; and also because it would have exposed the Christian message to the misconception that it was a political program.
While Yoder and others have gone some way towards undoing the latter assumption (that Christianity is completely unrelated to politics), I think that Bultman has a point. Jesus as King was a problematic proclamation outside of a specifically Jewish context, and remains problematic today. Scot McKnight's The King Jesus Gospel, while perhaps faithful to the original kerygma of the earliest Christians, has some questions hanging over it in terms of its usefulness today. (I haven't read the book, so perhaps these questions are raised and refuted within.)
Calling Jesus King, far from reinstating the politically subversive dimension of Christianity, actually has the opposite effect. In the New Testament, Jesus as King (or Jesus as Lord) functioned to undercut the authority of those who were known as Kings or Lords at the time, e.g. Herod and Caesar). To call Jesus one's King or Lord was to show the one's allegiances to him were in serious tension with the allegiances demanded by other kings and lords. Not so today (at least in countries without a monarchy). We can happily call Jesus our king, with this confession functioning entirely in the abstract. This is bad theology, because it is bad use of the language specific to our form-of-life that we have been given in which to think and speak theologically.
Speaking the gospel isn't about going back to the "original". That is the game of historians. This historical work is beneficial, but only up to a certain point. As (I think) Barth said, theology's task is to speak of God today. We do not ignore what was said earlier, but we do not copy and paste, either. On the surface, this is how I see the work of scholars such as McKnight and Wright. Their work is useful to the church, but perhaps not always in the way that they would imagine it to be.