A SBC-CSTM AC Superfast exp train should be run through the route Bangalore - Hubli - Madgaon - Mumbai. Although a little longer but since it supports high speeds between Madgaon - Mumbai(avg 90+), good speeds between Bangalore - Hubli(avg 70+), only 200 kms of bad stretch between Hubli - Madgaon, the time taken can be down to about 19 hrs. Starting 4 pm reaching Mumbai by 11 am.
IR should think of connecting the Golden quadrilateral NDLS - BCT - MAS(via SBC) - HWH - NDLS with trains having Rajdhani Status between sectors BCT - SBC - MAS - HWH which can be called Golden Quad Express.