Although I see the benefits of F/I, I see huge flaws in your thinking.That may be, but I can't comment on cars we don't get. If they had in fact perfected the technology, why not offer it in their 4, 6, and 8 cylinder engines? Why do they just keep increasing displacement to enhance performance? I think BMW broke with the pack when they held displacement of their famous I-6 at 3.0 liters, while adding twin turbochargers. And look at how successful they've been...now they're doing the same thing with their V8s, with MB following in their footsteps, leaving the Japanese in the dust.
First. BMW and MB have done nothing revolutionary here. Toyota's (2ZJ-GTE) I6 came out more then 15 years ago. BMW has wisely capitalized on this technology as concerns for fuel efficiency have increased in the public eye as gas prices have risen and the economy has fallen. As these concerns have spurred, 'large' displacement engines have become frowned upon. F/I is a cheap/effective way to increase power without the need to increase displacement. So instead of using new innovation to squeeze more power out per displacement, manufacturer's are slapping turbos and superchargers onto there existing motors. Yet, if it where all benefit and no drag I doubt the Japanese would avoid using it. The N54 was a great motor, but let's be real here, it had MANY reliability issues. BMW can advertise all day that the reasoning behind switching over to the N55 was for fuel efficiency reasons, but we all know it had to do with problems of the turbos. My uncle had 2 E60 535i's lemoned due to the same issue, misfiring in the turbo's. Now he is in a 2011 F10, we will see how the N55 performs. Also, you are incorrect when you say "the success of their twin-turbo's", as BMW has dropped the twin-turbo from the N54 and gone to a single for the N55. Yes, there are benefits to F/I but when you speak of the Japanese being left in the dust you are just speaking in ignorance. The German brands can afford to be unreliable, Lexus (Japanese brands) cannot.
Also. The 3.5L (2GR-FSE) on the Lexus IS350 returns 20/27 mpg, while the N55 on the 3 series returns 17/28, so I am failing to see what exactly you are going off about. An extra .5L is doing no harm, and for the most part is allowing for greater reliability on equal if not better efficiency. The use of "direct-injection" is an innovation that allows for more power and greater efficiency without increasing displacement.
This is no knock on BMW, I am a fan of their new engines and the use of F/I but to imply they have put others behind in the dust is just an incorrect assessment. I only used the N54/55 as an example because I have yet to here anything about Benz's new engines with F/I. The German's have done nothing revolutionary as of late with the application of F/I throughout there model line-ups. It is just a new trend, on the platform of already used technology.