Shatabdi express with 10ACC or 780 seats is already running. Tourists to Sikkim or Darjeeling won't prefer morning dep from NJP as they have to travel by road for 4 hours which is not possible during night and take the present Vande Bharat in afternoon. The Shatabdi express has current availability on many days for this 780 seats capacity in both directions. I'f a new VB is introduced from NJP morning dep then the travellers of Shatabdi will migrate and Shatabdi will be empty. There is no point of running 2 trains in direction one after another.