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Being from Dhanbad myself, I can understand why the original poster has suggested this series of extensions. However barring the suggestions numbered 1st and the 3rd , the others do not hold much substance.
It's easy to forget about ASN giving the dwindling number of trains at DHN. Though ASN has a much better connectivity when compared with DHN, just like DHN it suffers the fate of being delegated to a RLWL status or a PQWL status most of the times. The reason why extensions of the ASN-MAS & ASN-CSTM are virtually impossible are :-
1.>...
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ASN-MAS runs with a very high patronage from ASN itself and it is only a weekly train. There have been several attempts on ERs' part to change it into a biweekly but I don't see that happening anytime soon. The condition of the ASN-MAS SF is so bad that most people from ASN don't get confirmed seats and hence are forced to travel all the way to HWH by Coro or Mas mail.
2.> ASN-CSTM was introduced to compensate for the withdrawal of the tuesday service of the Imperial Mail via the mainline that had been forced by Lalu. Further the absence of proper mumbai bound train from areas like Chittaranjan, Deoghar and Giridih means that ASN-CSTM is not going anywhere...
3.> ASN-TATA could have been a valid demand however post the closure of the Dhanbad-Chandrapura line, most of the load that was catered by DHN has been heaped on the shoulders of the all ready overworked ASN Jn. I wholeheartedly agree to Sanjeev's sir assertion that the refusal to run more trains via Gomoh reflects ECR's incompetence and inefficiency, rather all of that extra load was forced upon Asansol that too via the single line between itself and Burnpur, that cannot be doubled without disrupting the life of a very large section of the city. So forget about introducing any other trains that have to reverse at ASN.
4.> ASN-TATA & ASN-SDAH both are ER's ASN divisions' trains, and while such a transfer into DHN ECR though definitely possible (happened with DHN-ASN passenger and GMO-BKRA passenger) seems very unlikely.
5.> However if shorted out, extending the Idea Express upto Dhanbad might not be at all a bad idea. Considering DHN's strong bengali populace and an already burdened Coalfield a intercity train via the main line is definitely required. With all due respect to HWH, getting in and around Kolkata and it's greater region is so much better from SDAH onwards. I remember that probably up and until 2016 the Idea Express didn't get much patronage given that it is heaviliy trolled post Bardhaman and especially after Bandel, and that Coalfield was very punctual. However since last year the Idea Express has suddenly been getting a high patronage from ASN itself. So I doubt it would be extended to DHN. If it were to be extended the number of coaches which are presently fifteen would need to rise.
6. > I am curious about the ASN-NJP Express! Did it ever materialize from ASN side or was it started at RNC post extension?

Be rest assured that though ASN is very well connected by railways the actual seat allotment is very less. Otherwise ASN would easily been an A1 station by now.