The planned gauge conversion of the existing Kolar-Chikballapur line appears meaningless & expensive since one wonders how useful it would be. How many trains will actually be run ? How many people will eventually travel between these two towns ?
It would make far better sense to provide a new line deviating from the existing Yelahanka-Chikballapur line, going past BIAL, crossing NH-207 (Hoskote-Chikballapur highway) at Sullibele, & reaching Kolar with much shorter distance. Trains can then be run between Bangarpet to Byappanahalli or even to Yeswantapur /City via Kolar, Sullibele, BIAL and Yelahanka.
This will also solve the problem of suburban rail connectivity to BIAL /DBP, etc. as also reduce train traffic cutting through the city along the City-Whitefield-Bangarpet line, which is already overcrowded.
Though HSRL is an expensive proposition, the value of a fast, dedicated rail connectivity for the airport for future needs of air travellers & employees working at the airport (& cargo complexes) cannot be over-emphasized, given that the airport is too far from city center - private parties have shown interest & HSRL can become a reality side by side with suburban rail.
Metro connectivity might not be viable since such high volumes might not become a reality anytime soon.