Aren't you supposed to demonstrate either a significant contribution in your area of expertise, or to charity or the community?
According to the Cabinet Office website, Knighthoods are awarded for "having a major contribution in any activity, usually at national level. Other people working in the nominee’s area will see their contribution as inspirational and significant, requiring commitment over a long period of time."
I'm no musician and haven't particularly followed his recent ventures, so can't comment on a professional level, but that's the benchmark he needs to work towards for a Knighthood. All I would say is, he's 39 and appears to have come to prominence in 2007; does 7-8 years (3-4 tours in military parlance) count as a long period of time? I would add that the same website's criteria for the BEM is "high impact work of a relatively a short duration e.g. 3-4 years." if that is any sort of reference to durations.