I think NON AC DD were tried before.
FLying Ranee between BCT and SUrat still has non AC DD coaches, and the train is very successful since ages.
Few years back, CST PUNE Sinhagad express also had NON AC DD coaches, but they have been withdrawn. The train is still packed to brim on a daily basis.
I only come to think that AC...
more... DD coaches were tried seeing the response to AC (overnight) express trains. But they have been tried in wrong sectors.
For example, INdore Bhopal DD is an epic failure so is the Dhanbad HWH DD.
however, on the other hand we have successful DD like BCT ADI/JP DEE and even the newly started LTT KRMI DD (holiday special).
So, I still believe, that if AC DD are started in the right sectors then it would work.