Considering it has single line, we can't think of all train. Moreover, it should benefit people of Tamil Nadu rather than Kerala. Their interest should be taken into consideration than any other states. The new line will help them to reach CBE, MTP faster, even trains via Konkan to Mumbai, Gujarat etc from TEN. This will help interior TN to get connected via shorter route. I guess, we should think in tamil nadu's perspective.
For Kerala people, they can get down at SRR or PGT, get the connection and travel. During MG time, thats how it worked. PGT acted as transit point.