Well none of this should be a surprise, it has been well known that turning up the boost pressure on Turbos ruins emissions (despite probably CO2 as such remains low at cycle testing), so making engines even smaller or making them motivate bigger cars will not work when more and more stringent levels of NOx, particles etc. have to be met. Diesels already have actually reached the level where making them any cleaner (or meeting real life cycles) involves cost that makes them more expensive then alternative solutions like hybrids or fully electric cars.
The proposed solution of an electric motor basically assisting like a turbo instead of a full flagged hybrid/electric car is an interesting solution of combining "greener" NA engines (esp. Atkinson cycle) and the "punch" of modern turbo engines, and it shouldn't brake the bank.