Why not make the gran coupe and the GT a 4-series, leave the rest 3-series? If they're all 3-series, then it'll just get so confusing (like Porsche to non-enthusiasts).
"What do you drive?"
"I drive a 3 series BMW"
"Which 3 series?"
"What do you mean?"
"well, do you drive a: sedan, wagon/touring, coupe, convertible, gran coupe, or gt?"
That is 6 models under the same designation. It is just too many. They have a choice to make, but I do not think that they know which is best yet.