First use existing line, then explore new one
how come. KIA to YNK ka line will be feasible as YNK is only 15 kms away from KIA.
Line is already present, just double it till Devanahalli from Yelhanka and they should construct a halt station ('Yerthiganahalli'/'Udayagiri') near Anjaneya temple beside trumpet flyover and provide shuttle bus services to and from airport ~4 km, that's over. There is no strong will from govt, otherwise this would have been reality today.