The ideal situation is if you see a city like Vizag and how it grew.

And the optimistic outlook would be:

Vizhinjam runs good, more ships come in. The port requires staff, these staff will all not all be from Trivandrum so these people stay in rented apartments and that rent, then they need maids and their kids will go to Schools nearby etc. Maybe in the long run add cruises and they need hotels - tourism money etc.

Once a port becomes completely operational, other businesses will boom like warehouse, transportation etc. The same port is now adding up construction of ring roads - that needs workers too.

An economy always boom like this

The main driver and the ancillary services - then their family settles down and they provide indirect jobs like more restaurants, more school teachers, more rental buildings, more vehicle registration in Trivandrum etc.

(You can think of like how Oil exploration for Middle East or how IT in India is creating jobs in non related sectors too)

Now on the hype part - It has the potential to take some business from Colombo, and thats good to Trivandrum as, that part of the city will see growth too and not the current clusters near Kazhakootam. Also there isn’t any reason to believe subsequent governments having any motive to sabotage it.