Personally I wouldn´t mind at all if Michael had just been called "The King". However, those of us who are familiar with the term "positioning" within marketing will know that the use of the title "The King" will never be used by the huge masses on MJ, that title is taken by Elvis, and I think it will always be that way. I mean, we as fans can call him the King, but on a wider scale it will not spread out. Which I in a way think is okay. Let´s let Elvis keep that and have another title for MJ.
If "The King of Pop" is no longer suitable for MJ then one would have to take a title that is not already taken. I think "King of Music" is a great title for Michael Jackson, although he certainly also is the King of Entertainment I would go for the music thing. But repositioning is usually very hard when a name has stuck to a person, so I guess "The King of Pop" will still be the mostly used title when referring to MJ.