(1) Gatiman's speciality is it being a super premium train(much better than Shatabdi). Its fares are higher than Shatabdi due to much superior on board facilities/food and train host/hostess. AC DD is a higher volume and inferior travel than normal ACC and its fares should have been kept a bit lower than ACC. So ACDD coaches in Gatiman shall go against its super luxury status. (I wonder what would be difference between the Gatiman & proposed Tejas & Shatabdi of course)
(2) Mumbai-Pune is excellent destination for ACDD but existing rail route is longer than Mum-Pune express way route, it is full of curves and steep gradients since it was planned and constructed about 150 years ago. A cumulative effect is much...
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higher journey time than buses/ cars. So major traffic is on the Mum-Pune expressway
Today a straight rail track without curves and gradients but with longer tunnel route & without any speed restrictions/ banking loco is possible. Such track shall have higher initial cost but the recurring saving of fuel cost, journey time, operation/maintenance cost shall make it a better option.
I personally wish that instead of extra track from Kalyan-Pune, IR should construct straighter route from LTT to Pune via thane creek which may be any where around 120-140km long. This may run parallel to existing tracks for some length (LTT-Vashi, and for some distance from Pune along Pune-Karjat line) and run 160kmph+ full ac trains (60-90 minute journey for non stop/with stops journey) and 130kmph non ac LHB trains (75-105 minute journey) in large numbers. Passenger response to these "desi bullet trains" shall give a good indication whether bullet trains for about 500km journey shall be be successful in India or not?

I agree that Gatimaan is super luxurious train. But to increase the tourism in Agra, a normal AC Superfast train could serve the purpose. AC DD can in fact make 2 rounds to Agra in a day. The journey time of 2 hrs could also not be a issue for those uncomfortable seats of DD.
Your second point of a new track between Pune and Mumbai. This is apart from a costly affair, not a immediate solution. They can attract passengers on this route by offering a ticket price lower than Volvo bus and lesser journey time by traveling via Panvel Vashi to Kurla and Dadar with halts at Panvel and Vashi. AC DD via Vashi sounds odd but worth giving...
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a thought.