Thanks for taking the efforts and sharing the information, sir!
You are partly correct. The North-South MG link was in consideration from 1904 itself. While the route was opened fully in 1928, construction started before 1910. KRNT-DHNE section was opened in 1909. PAU-Hingoli was also constructed in parallel and opened in 1912. After that there was a long gap. As I said, the onset of World war 1 and change in British priorities put these projects on the backseat and further construction went on only in bits and pieces. SC-MBNR was delayed by the war and completed in 1916, but the remainder of the link was only completed 12 years later. On the North end...
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the link wasn't even completed until 1960.
The C.T.Walker survey isn't the only survey that was carried out. When the Gadag-Wadi (The line was called by this name only, irrespective of the take-off point in different surveys) line was not sanctioned, more surveys were carried out in the same time period (Raibag-Bagalkot-Hunagund-Ilkal, Raichur-Koppal, Raichur-Sindhanur-Kushtagi-Badami being the notable ones), but the Madras-Bombay route was never particularly favored by the British, and none of these saw the light of the day, despite being requested for, from the late 1920's.