V6 engine for the M3 is the worst idea I ever heard (that is, after RFT tires and electric power steering). Its simply an inferior layout from a balance point of view. I'd much prefer to see an inline-6 engine being used. That is the best way to make a smooth engine with a nice exhaust sound. V6 engines generally don't sound the best.
If not an inline-6, they should simply drop in the turbo V8 from the M5 - End of topic!