Today I was told by Dr. Nietzsche in M Experience in Istanbul that a lighter version is coming but we shouldn't expect anything more than 50-60kg reduction over the standard car. Most of these weight savings is expected to come from lightweight front seats and rear seat delete. As others have stated the car has a LOT of lightweight features already.
Although he said that BMW M is in a R&D status on CF wheels but it might be another generation away...