According to author VB are designed as set of 4 coaches and eqxh section is powered by an independent motor so augmentation, power and performance would not be an issue. So RB are asked ICF to prepare for plan for 20 coaches. It's not clear whether RB has to manufacture new sets or augment exiting sets with another 4 coaches to successful 8 and 16 coaches as it's insider information and no official document.
According to me yhe VB which can be made 20 coach are
1. New Delhi Varanasi Morning dep...
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2. New Delhi SVDK Morning dep
3. Mumbai Gandhinagar
4. Ahmedabad Mumbai( though it's new the quota system is divided into equal parts with Surat as charting)
Except these 4 no other VB will have good occupancy I'm all seasons for a 20 coach. Every route has an off season ranging from 3-5 months and welders only one directions and didn't get back travellers in last sections.
Coming to 8 coach to 12 coach
1. Dehradun ANVT
2. Amritsar Delhi
3. Kasargod TVM Morning dep
4. Coimbatore Chennai
5. Turunelveli Chennai
6. Kacheguda Yesvantpur
7. Mbai Madgaon.
8. Patna Howrah.