Double Decker will be success in those areas were people largely travel in AC coaches that is Delhi, Mumbai and Kolkata. But Kolkata DD was flop due to the Dhanbad if they have made it to some other destination, then it ould be good.Already there are large number of trains to the Bangalore from Chennai with 2 being Shatabdi express. I know it will take time to get success,People in Tamil Nadu and Karnataka travel mostly in Night Trains which are sleeper classes.Ok now you can take an example trains from Coimbatore to Chennai includes 2 Second Sitting trains and other as sleeper Class, but the second sitting in Intercity Express is not good as Kovai Express because Kovai Express has seats which give rest to back. So if you see the trains like Cheran, Nilgiri, are always full. DD will remain white elephant for few months till people wish...
more... to travel. Many people will travel in large only for few weeks because to enjoy DD, after that....../ Because seats in Shatabdi are comfortable compared to DD. DD has less leg space.