I agree that M2 buyers probably aren't all that concerned with fuel economy, but the other part of the argument is, I believe, where this reasoning falls down.
Fuel economy is very tightly linked to weight. F=ma, and all that jazz. Driving a car is a repetitive process of accelerating the mass of the car to operating speed, then slowing it down again. Outside of hybrid cars, the slowing part wastes all the energy you've input, so all things being equal (engine efficiency, aerodynamics, driving style, driving route), a car of greater weight will have worse fuel economy.
I think you grossly underestimate how poor the fuel economy of high-revving engines is and its impact on fleet averages and sales. While M2 enthusiast consumers might not be focused on fuel economy, it would definitely have an impact in the overall market. When your average joe M2 buyer compares the M2 to the CLA45 AMG and S3, a huge difference in fuel economy would have them scratching their head. Have a look at the typical numbers for N/A vs FI:
E92 M3 (3704 lbs): 14/20 mpg
E46 M3 (3415 lbs): 14/22 mpg
E82 1M (3362 lbs): 19/26 mpg
On the city side of the equation, the 1M Coupe sees a 36% improvement in fuel economy[1] for a 2% reduction in weight[2]. Do you think BMW can afford to leave a 36% improvement on the table in a competitive market?
1: (19 - 14)/14
2: (3415 - 3362)/3415
You sound like an intelligent guy. I don't mean to insult your intelligence in any way, but I think you're running in to a bias called the
Dunning-Kruger effect. What you don't know about engine design is affecting your ability to reason through this, but you aren't factoring in that you don't know much about engine design.
I'm not saying that they couldn't take the N55 block and make a N/A engine from it. What I'm saying is that you underestimate the number of changes required to do that, and you overestimate the quality of the outcome. When you turbocharge an engine, you are forcing air through the engine. This is fundamentally different than a N/A engine.
Engineering is full of compromises. You want components to be light, but you also want them to be strong. You want them to be light and strong, but you can't make the entire engine from titanium because it would make the engine too expensive to produce. So, you compromise.
When you turbocharge an engine, you're changing the intake pressure from a negative value to a positive one. Go read up on that Autozine Technical site about the challenges first encountered when manufacturers started putting four valves in an engine. Read about the compromises and solutions they came up with. Now, recognize that when you turbocharge an engine, you have a completely different set of compromises to make.
For example the temperature the exhaust gas around the exhaust valve of a naturally aspirated engine gets hot, but it doesn't get anywhere
near as hot as a turbocharged engine. The exhaust area of a turbocharged engine gets hot enough to cause a huge cast iron manifold to glow. A standard mild steel exhaust manifold would literally melt under the heat and pressure. Because of this, you want extra cooling around the exhaust manifold, so the heads on a turbocharged engine will have larger water jackets to keep the exhaust valve area from self-destructing. Larger water jackets must be fed by larger water exchange ports between the block and the head. Larger exchange ports mean more water must be supplied by the water pump... and down the rabbit hole we go.
That is just one example. There are a series of cascading engineering considerations that
should be made in order to build a turbocharged engine that is reliable enough for a production car. The changes aren't huge, but they're numerous. It's not like a turbocharged engine block can't be used for a high-revving N/A setup; it's just that it's not optimal.
There is a way. There is always a way. But the engine you're describing would be
far more bespoke than, for example, the differences between the N55 and the S55.
Naturally aspirated engines are a thing of the past. Their fuel economy is too poor, and the automotive press, as well as consumers, have fallen in love with the day-to-day drivability of a turbocharged engine with a fat torque curve. The vast majority of consumers (including M buyers) will read the latest review in Road & Track/Car & Driver/Automobile/etc and believe what is written on the page. Given how well reviewed the current crop of turbocharged engine powered sport compacts have been, why would BMW take a flier on a formula that is clearly on the wane (from a market perspective)?
If your position hinges upon profitability, then BMW need not be concerned about alienating the enthusiast market, because the enthusiast market is so tiny that its effect on sales would be measured in basis-points, not percentages.
Man, it's awesome to read something so nostalgic. BMWs haven't been sold on racing and M heritage for a long while. What do you think BMW's marketing budget was last year? How closely related do you think the BMW Z4 GTLM/GT3 or BMW M3 DTM car is to the road car? How well attuned do you think the average consumer is to the reliability of those cars from a motorsport perspective?
The reputation of BMW's past will carry it much further than you think. It can do this because of their marketing engine. BMW doesn't have to produce another E30 M3, because their marketing engine can just throw up a well produced video of the E30 M3 next to whatever new car they're selling, creating an emotional connection in the minds of consumers.
I think the new M2, M3, and M4 are going to be fantastic cars. I think they're going to be well reviewed, and I think they're going to sell better than any M-cars before them. I do not, however, think they'll be very much like the M-cars of the past. That is the way of progress. You can choose to embrace it or to fight it, but you cannot stop it.