The only challenge a reverse VB from SVDK is that at 6 AM early morning, tourists/ pilgrims don't depart. Most complete their Mata Vaishno Devi journey back to Katra in the morning hours. Dont think anyone prefers to leave so early in a day sitting train without rest. And the ones who have completed previous evening, they have plenty of late night trains to depart for Delhi with a sleeper bedding to have additional rest.
Though from Jammu & Ludhiana it can still get decent patronage towards Delhi in the morning hours....
more... Possibly a 8 coacher would be enough in that case. Better to run it as Jammu-Delhi VB with additional stoppages at Pathankot Cantt, Jalandhar Cantt, and Panipat.
The existing VB leaving at 3 PM from SVDK gets good response because tourists have had rest for 4-5 hours, and 12 PM is the time when Hotel check outs start.