If really they want to save 20 minutes, then avoid loco change at Igatpuri, let WCAM 3 haul the train till Itarsi. Use WDP for better acceleration and speed. Even at diversion route i think all the train will be made to hault atleast for minimum 10 minutes till it get clearance to enter in to main route.
This diversion will really increase the load on other train going towards Allahabad. I have seen that many people avoid to board LTT-BSB Sf Exp, LTT-PNBE Sf Exp, LTT-Guwahati Exp, because they actually do not want deboard the train at Cheoki because of reasons already mentioned previously. Infact Mahanagri get more patronage from Allahabad as compare to Varanasi.