I can't see the politicians going for that one, placing the armed forces out of direct political control. The COS would obviously oppose all attempts to cut his budget which wouldn't suit any party. As a non-MP he wouldn't be able to answer questions in Parliament either which would mean that someone else would have to do so instead - PM or Foreign Sec? Defence would therefore lose its direct voice in the House of Commons. It would also mean that the Head of the Armed Forces was an appointee rather than elected which is not really the way our democracy functions.
Still, given the irrelevance that defence commands in the eyes of most of the population & its elected representatives then perhaps removing it from their immediate sight would not be a bad thing, they could continue to ignore it until such time that they might want to invade or attack something.