Sorry, I haven't read all the posts on this thread, but for what it's worth....
"BMW has reversed its notion to rename the supercoupe M4 because there's too much equity in the M3 name. While the plan was to give even numbers to all coupe lines, like 6 Series and 2 Series, BMW might scrap the 4 Series name for the two-door that enters production about a year after the all-new 2006 3 Series sedan, again, because of the respect earned by its current brand name." - Motor Trend (Sept 2004)