Ajanta was always MMR-SC/KCG only. Due to GC it used to short terminate for sometime at Purna/NED/NZB as link expresses. Same with Devagiri. Both were originally intended for SC only.
A few south bound trains can originate from NZB now that the PDPL line almost complete. Since NED is very close by, I doubt if SCR will be interested in developing pit lines again at NZB. But other than to destinations like SC, neither NED or NZB can completely fill a train all by itself to most destinations. So it isn't much of a loss if some trains just pass through. Usually most the trains to NZB, NED from south have a lot of people traveling...
more... to SC who will eat up lion's share of the quota. Not much quota lost by extending to NED I guess ( Correct me if i am mistaken).
More important is that more south bound trains be provided via the new PDPL line to give more quota to NZB, which otherwise would end up being used as trains to SC by most passengers.