Reduction of Kolkata-Agartala distance from 1613 to only 513km is awesome, but there are many practical issues to be addressed before commercial operation of Kolkata-(Bangladesh BD)-Agartala train could begin, like safety, smuggling, human trafficking etc. It will be interesting to know how the train operation shall actually done via BD. Shall the train operated jointly or it will be a JV between Indian & Bangladesh Rlys??
Since about 90% of run is likely to be in BD territory, shall the train stop at Bangladesh station or the train has to be a Duronto type without stoppage in BD.
Or...
more... there may be some trains with one destination in India and other in BD and some (Kolkata-Agartala) crossing Bangladesh nonstop.
Running speed/ avg speed, priority in BR Rly network etc are factors beyond control of IR. What shall be the speed/avg speed/ Journey time.