How long is this route compared to the other 2 routes? Also, since this is a single electric line, I think, I don't think many trains will run. Maybe one train that starts at evening from LJN, reaches Mailani before midnight will be of convenience to both Sitapur and Mailani passengers to reach Delhi.
I don't think Shatabdi will be shifted since it has been running on it's original route for over 3 decades now.