Not only towards north east even locations of Bihar and west bengal after Patna lacks connectivity from Mumbai. I think if new train can't be introduced then they can atleast do the following:-
1. All train should have a minimum distance restriction for reserved classes like in Karnataka & Telangana Express.
2. 15645,15647 & 12515 should have a technical halts between MGS and PNBE (much better if they reduce halts and convert 15645 & 15647 into SF) so that Mumbai to Patna pax should not board this train.
3....
more... Divert 22511 Karmabhoomi Express via Purulia, Adra and Asansol with Loco change at Andal. (Kolkata pax can be avoided)
4. Increase the frequency of all these trains as much as possible.
5. Extend any one of these trains upto DBRG, AGTL, SCL or NTSK.