Insideline actually gets this right when they state, "The absence of a Z4M is made more surprising by BMW's decision to develop a customer racecar based on the roadster." BMW is already racing an M version of the Z4. They produced an M version with the previous generation. They produced an M version with the Z3 that preceded it. Do M SUV's really make more sense than a dedicated sports car? For the BMW M division? The world has flipped upside down.
If the folding hardtop were to be ditched to make a new M coupe not only would the car be significantly lighter than it is, we would have a modern BMW sports car offering far greater agility and rigidity than the Z8 could have ever dreamed of even at a much higher price point. This is the car BMW should already be making. The fact it is still being debated internally shows how far BMW M has gotten from their principles. Throw the 550 GT off a cliff (nobody will miss it) and bring us something like what is pictured below. Just give it a real M motor (4.4 liter S65 from the M3 GTS would be what the real M we used to know would do) and your first customer is right here.