If the Asn-Bsb VB runs via GC, then I don't think it would be able to fetch much passengers. Honestly Asansol and Dhanbad together won't be able to fill up a whole VB for Varanasi.
Rather Asn-Bsb VB should run via Patna. Asansol - Patna section has a pretty good demand and can ensure a steady flow of passengers. Infact Indigo is recently launching direct flights between Andal and Patna after sensing the high demand of this sector. Railways should also try to cash in on that demand.