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People in the USA have a bad collective memory about diesels, due largely to poor experience with them in the early 80s. They were dirty, loud, rough, and worst of all, slow as molasses. My dad had a Mercedes 300 CD, '79 or '80I think, that had a 5 cylinder non-turbo diesel. It did O-60 MPH in "I'll get back to you" and it sounded a lot like a truck, but otherwise it was a pretty good car. A friend's parents had a Buick Park Avenue with one of the GM gas conversion diesels, and it was absolute junk. There are plenty of those 1970's and 1980's European diesels still on the road, but I'd bet it would be hard to find any of the American models in active use.
Regarding the redline, I drove both a Porsche GT3 Cup Car and a Dodge Viper Competition Coupe in the Speed World Challenge in 2005 and 2006. I was a Porsche fan and thought that it was a blast revving the modified GT3 engine to 8400 RPM or so, pumping out 450+ HP and requiring earplugs. When I first drove the Viper I was convinced that I wouldn't like it, what with it's "truck" engine and 'murican pedigree. After 5 laps on a cold January day I was able to match my best time ever in the GT3, and I came to really appreciate what torque meant in a race car. Looking at the MoTeC data showed how I was "working" like crazy to keep the GT3 in the powerband, while in the Viper I could leave it in 3rd gear for everything but the long straights. I'm sure that a really good driver could go fast in either car, but most any driver can go faster with a lot less effort in the Viper.
How does this relate to the discussion? High revving engines make interesting sounds and you might think that you're going faster, but that's not always the case. The Viper's redline is ~6000 RPM, but it's rare that you'd actually need to rev it that high because it isn't going to make you any faster. The "diesel like" torque curve allows the car to be effective from 1500 to 4500 RPM, and you can use the throttle to control the car without shifting like mad at every corner entry and exit. I still love the sound of a high-revving Ferrari, Porsche, or BMW GT car, but I now better appreciate that this isn't the only or best way to make power.
What BMW should consider is how to tune the sound of the diesel engine and combine it with a "Doppel-U / min" tachometer setting. The driver would see 2X the actual RPM, and would hear a higher-pitched "scream" to match, with the goal being to emulate the experience of driving a higher-revving gas engine. This isn't all that far removed from some of the initiatives to add sound to the hybrid engines, which are primarily focused on safety, although in theory they could emulate almost anything. With DCT transmissions and the various control mechanisms in modern cars it may be that almost any sort of experience could be available. While this may be too videogame-like for some, the fact is that most/all cars are becoming more like this over time. The accuracy of the simulation could be a great selling point, with the "M" cars providing a better simulation than the standard cars.
If you were to fast-forward and could drive a hypothetical 2015 M3, would it matter how it was powered if it was more fun than the current generation? A sub-3000 lb. weight with a 350HP 2.0L 4-cylinder tri-turbodiesel with KERS and more would probably be a lot of fun. The fact that it could also easily get 30+ MPG in the city and over 40 MPG on the highway wouldn't be a bad thing either.
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