This wont happen. Practically not possible and wont benefit people in any case. In a regular Express train if people travel, they will reach in about 1 hrs 10 min. The metro for such a huge distance of more than 70k will have many stops and practically wont benefit. The cost for 1 km is 250 crore so one can imagine what the cost will be for such a long distance. Up till Kochi airport they can possibly try but even then that will also be a huge expenditure