BMW wouldn't be committing any bigger crime by going for bi-turbo V6 engine, more than they have already sinned with the turbos for their M cars. BMW M cars were known as high revving NA I6, V8 and V10 engines with supreme agility and control. Now they've chosen to use turbos in their M cars? BMW also used to be known for manual transmissions in their M cars. But now they use M-DCT. Now they even have X5/X6 M's but no Z4 M.....
I think everyone should get ready for a bi-turbo V6 in the F3x M3. It might just be another masterpiece engine from the M division. Look at the bright side - it would definitely be a unique BMW engine.