There are two issues. This time slot is highly constrained with multiple Mail trains/ICE/VB already jostling for space. Second, IR won't use this route since it bypasses Lucknow [they hardly even use it for trains that do not get significant patronage from the state capital, let alone a day time VB]. Also, the BUW-STP-SPN line is currently still quite slow. I think IR has recently doubled the BUW-STP section but I am not sure of the mps. This route definitely needs more trains but this imaginary train is unlikely to happen [just like how RNC-BSB VB does not use the shortest line just because it'll have to bypass couple of important stations].