This superb new I6 diesel is now out in Europe, (not sure about NA) . Currently in the UK it's only available in the CLS in 350d and 400d 4 matic forms, and in the S350d.
I think in Germany the S400d is also offered.
In 400d form it makes an incredible 340bhp and 516 lb ft of torque , which is incredible considering its 2.9L capacity ( compare that to some older NA V8 petrol engines).
Given that the CLS and E Class share the same chassis, it's a bit perplexing that Merc are only offering this new engines in the 2 models for now, and the E Class is still only offered with the old V6 Diesel, which is now pretty ancient ( the OM642 has been out since 2005).
The same strategy is also mirrored with the V6 petrol turbo, which is still offered in some markets in the E and S in many markets despite Germany being offered the new in line 6 petrol, in the CLS and S Class .

I would be interested in an E400d 4 Matic, or at least the 350d , does anyone know the reasoning for it and also when the E will get this engine?
I don't think its for testing reliability in lower sales models first either, because in Europe the S350d is a huge seller and that's already offered with the new in line 6 diesel as above.

In the US Mercedes does not offer any diesels for passenger cars, only trucks and Sprinters.