This entire thing could be fulfilled by a reverse Vande Bharat Express or IRCTC Tejas from Varanasi (morning departure)
I'm sincerely against extension of Duronto being a regular user myself, having an upcoming trip in same on 7th May.
But if Prayagraj is going after Kanpur Shatabdi
Then Prayagraj LTT Duronto and Prayagraj Ahmedabad Express should be speeded up and extended till Kanpur...
more... Central with 50% Quota reserved for Prayagraj.
Kanpur is a big City itself, cannot be taken for granted everytime by Prayagraj. Already they had given Udhampur Express to Prayagraj. In extended Kanpur Shatabdi 50% Quota should be reserved for Kanpur Central.
It should be give and take.
Don't get the sense behind demanding a fully AC Shatabdi for Lucknow. It should be at most a Jan Shatabdi to ensure proper patronage. Shatabdi would need involvement of both Varanasi and Kanpur to be of any success.