Netravathi Exp , Kerala Exp and Trivandrum Mail are the only 3 trains in Kerala to have four 3AC coaches. I dont think additional 3AC coach would be added. Maybe an extra sleeper coach can be added. Many new trains are having at least 4-5 general coaches. Netravathi could also add additional 2 unreserved coaches because i have seen lot of passengers entering sleeper coaches during heavy rush time since there is no place in general coaches and only 1 unreserved coach is available at either of the ends