(Diesel) Loco-hauled trains for serious commuter service is kind of a joke anyways. If it has to be diesel-hauled, it would mean DMUs. But electrification is better anyway, not necessarily considering air quality (where those statements that Tier 4 is very good… simple chemistry shows that they produce tons of CO2; what is taken care of with modern technology is the NOx and to some extent the particules. Sulfur is taken care of with low-sulfur fuel.

As it has been stated, electrification's justification lies elsewhere. Partial electrification is a bit of a kludge, but may be justifiable to some extent.

Now, there are several manufacturers who have DEMUs in their program; just recently, it was Stadler who got a nice order from two operators in the UK for FLIRTs with a diesel pack, which is in its own carbody, shorter, but just like a regular passenger carbody. Power is, of course, limited, compared to the electric part, but it is accepted by the operators (and still has better specific power (kw/t) than what Metrolink is hauling around with locomotives).