WIth a reactor on board, you can stay underwater until you run out of food for the crew. You won't run out of motive power, or air, or drinking water before you run out of food. You can literally stay submerged for months without surfacing once.
I'm not terribly afraid of India. In fact, I think they're a natural ally -- they're threatened by China more immediately than we are. And if they can carry more of the freight for patrolling the Indian Ocean and the southwestern Pacific, more power to 'em.
But on the other hand, another country with boomers means more targets to track that aren't easy to track, and as we've learned from bitter experience, many times at great cost, yesterday's friends aren't always tomorrow's.
It just needs enough stealth to prevent detection by Chinese vessels.