They give a hint in the paper...
the clatter in diesels is due to the fact that the fuel has to evaporate and mix to the point that there's enough around stoichiometric for combustion to start...and when it does, it geos off with a bang...Peugeot have up to 7 individual injections in a single firing stroke to try control it.
The HCCI diesels are trying to get rid of that. Ford is doing a lot of development with them. Essentially, they inject a small "starter" amount of fuel, then inject the fuel charge after it starts to combust.
We will see diesels lower compression ratios, while gasoline engines continue to raise them. The designs of diesels have a lot of "baked in" goodies that improve fuel economy - like not needing a throttle. Compression ignited gasoline engines will give us a lot of benefits in both power and economy (think about the torque that diesels make).
I wish I had my ICE engineering design book on hand so I could screen shot some pages.