There is enough rush between Mysore and Bangalore. Any new train will be patronized well. If I am not wrong, KSRTC Non A/C express fare for Mysore is around 170Rs. At 260Rs for A/C this is quite an attractive option for most people.
Also, even if it doesn't work out, Railways have nothing to lose. They are just arranging for people to book these berths instead of just letting the train continue with empty berths between SBC-MYS. It's a win-win situation for both the passengers and the railways.