your reply has so much logic and sense in it that i'm pretty sure it will never be implemented by IR.
To add to your answer, the major workshops for manufacturing should also be zone wise (zones as per your scheme, not the current ones) so that the needs of the zone can be fulfiled internally rather than begging at RB's door for every small thing. For inter zone trains have centralized workshops.
But again i'll reiterate, such a logical step will never be taken by IR.