In terms of background information, the C-scale refers to an early attempt to classify congregations or ‘Christ following communities’ (but not ‘churches’) according to how ‘contextualized’ they are. The word ‘contextualization’ originates with the educational and missiological theory of Shoki Coe (1973, 1974), a Taiwanese pastor and educator, and in its original form envisioned the next step beyond indigenization. That is, contextualization was something done by the indigenous Christians, it was not done for them. By the time that Travis devised his scale, which ranged from c1 (a church speaking a foreign language and Christians exist as an ethnic/religious minority) to c5 (people who identify themselves as Muslims of some kind and use the religious and cultural forms of Islam, and remain culturally and officially Muslim). Western evangelicals had lost the original (Asian) meaning of contextualization and had instead decided that contextualization was something to be done by missionaries for people of other cultures. The intention behind this was to ensure that the Good News would reach people in a cultural and religious form that would not be objectionable to them. This vision of contextualization (in Islamic contexts, at least) placed a great deal of emphasis on how people dress, what greetings they use, whether or not they eat pork or drink alcohol, whether their women cover their heads, and so on. Some missionaries even went so far as to legally convert to Islam so they could be a Muslim to the Muslims, in their attempt to imitate St Paul’s own practice (1 Cor 9:20). This concept, that a Muslim (or Buddhist or Hindu or Taoist) can follow Jesus while remaining an ‘insider’ to their religious community is at the heart of so much debate today, and Dr Dixon shares his insights on the topic in the interview.
Read the whole article/interview, in the Journal of Asian Mission, a publication of the Asia Theological Association, of which NETS is a member. Links for the PDF can be found at academia.edu or Miller's blog.
 Some (like Travis 2000) have advanced the unfortunate term ‘Messianic Muslims’ for such people. All Muslims, though, accord the title ‘Messiah’ to Jesus son of Mary, so technically, all Muslims are already Messianic.