So I guess one might have to still wait for some time to see two separate rakes for DHN-Alleppey & Tata-Alleppey.
Here is the response from railway authorities on having raised the issue in the grievance portal
• For the passenger of Jharkhand desires of travelling to South part of the country, a new train between Hatia and Ernakulam will be introduced subject to availability of rolling stock
• Separate...
more... running of 13351/13352 Dhanbad-Alleppey Express and 18189/18190 Tatanagar-Alleppey Express is not operationally feasible at present.
The new train may not benefit people from Tata, may not run daily and may not touch Chennai. We have to still wait and watch. Even railways does not seem to have any update on its introduction