Like by the time Jabalpur Balaghat Gondia Gauge conversion finishes Jabalpur would probably get electrified so if the the Railways wants to use the new line (for both freight and passengers) they would use diesel (adding to more cost). Then some years later she to increasing traffic they would sanction the doubling and electrification of the track (costing more due to inflation and already used Diesel). So better to electrify and double it simultaneously.
Rail fans from Jabalpur could shed more light into this matter