Even 8C will take some time and festive seasons to catch up with the bookings. Durg-Visakhapatnam, Howrah-Gaya both of these trains require a rake change to 8C. It'll be interesting to see on which route will ER use the 20C rake.
I don't think they've abundance of 8C rakes at present. New unpopular services like LKO-MTC and TATA-BAM are running with two dedicated rakes. That's the reason BSBS-AGC Vande Bharat's regular run has been postponed to August 23, because the rake has some technical issues and they don't have extra rakes handy.