I love convertibles, but the weight, handling and performance penalty bothers me a lot. That's why I passed on the M6 Convertible. Unless M performs some special magic on the M3 Convertible implementation, I will likely pass on that too.
However, if the rumored Z4 M Roadster comes out with the new V8, that would be impossible for me to pass up. Unlike the 3-series, the Z4 was designed to be a roadster. The roadster version of the Z4 M actually weighs 33 lbs less than its Z4 M Coupe sibling. While I believe the Coupe handles better, the convertible penalty is way lower here than elsewhere in the BMW line.