Did you know that the Ganga & Kaveri rivers are connected? ... by Mysore Varanasi Express - Vishwanath Joshi

He is talking about sanctioned projects, so he might be right. There are many more older proposals, that were surveyed, but never sanctioned officially.
The KCG-GTL line is not related to the Wadi-Gadag line actually. Both were independent projects proposed for different reasons.
The line initially surveyed was Wadi-Koppal (Reconnaissance survey carried out in 1906), mainly for famine relief and mineral transport. Since the entire interior Karnataka region was on the meter gauge, this line was also proposed to be on the meter gauge (passenger traffic...
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wasn't expected much from the hinterlands on the Madras-Bombay route). But this would necessitate a change of gauge at Wadi and the Nizam's state railway was expected to bear the cost of transshipment and other facilities.At this time, the Nizam was also being forced by the British to use his MG network to connect the North-South MG networks and plans were already drawn to construct an MG link between Mahbubnagar and KRNT ( GTL-Dhone was already operational for 2 decades by then, Dhone-KRNT under construction by the SMR and Kurnool district board and SC-MBNR was being constructed for expanding services in the Nizam's dominion). But the onset of World War 1 made the British change their priorities and focus shifted to the BG routes for Coal and mineral traffic.