Its not threatening US, but safeguarding our national security. India won't be using any nuclear missile anyway that doesn't mean we must stop producing it, icbm is just a show of capability to strike anywhere in the globe and to be a superpower we must posses that capability.
Its not like as of now India would produce it, we are not a superpower now, but we will be in future if we continue the way we are going or better, it has to be gradual, may be 15 years from now, if nuclear subs are so capable then i guess China invested badly.
That's right we have to prioritize our needs,
After A5 , so far as missile range is concerned , it is sufficient to fulfill our operational needs , what we do at this point is miniaturization and evolution.
putting the A5 on nuclear submarines would be our first priority.
If we accomplished that the Tech would have been miniaturized to what we need.
Making a longer range missile then only becomes a matter of organizing more funding , with the only incentive being this new missile will take in design advanced made in the last few years