I Also heard of a 800cc Triple Cylinder Diesel bike, that made just 54 bhp, but its Torque was way high at 150 NM. This was sometime back in 2007.
Say if a 800cc gives 50 bhp, what do you expect a 100cc to give? 4-5 bhp at the most ...? Moreover, Fuel Injection is a costly technology, but a compulsory one for Diesel Engines.
You see, such engines are very torquey, and can't give a relatively high amount of power for a particular cc, compared to Petrol Engines. Although for Cruisers, it makes sense though.
BTW A guy named Balu is changing the world with his Diesel & Bio Fuel Enfields, with his group Bulletwallas... See this site:-->
The World According to Bulletwallas: April 2009
He says that the guys at Enfield are not supporting him, despite a great machine & plan... So, I guess it won't make it to production ...