Both Rajdhani and Shatabdi are meant to provide fastest available service between capitals/cities. BPL & LKO attain that via Shatabdi. But since Shatabdi returns on a same day, 10+10+Maintenance would not have been feasible as per concept of train, isilye Rajdhani chalaya. And ye pattern Jaipur, Chandigarh k liye bhi follow kiya gaya.
So there is no point in violating a concept of a premium and most reputed train. An AC Duronto that has similar priority as Rajdhani can be discussed.