We are already developing the A5 , it will cover all security concerned by bring into range almost any viable target.
Being Canister-ed it could also potentially be made into an SLBM , which would be our next priority.
Combine that with might of the Surface fleet of the India Navy , along with its own Long range Missiles(Such as Nirbhay) as well as Ship launched Ballistic Missiles like Dashun,
Indian forces can strike almost anywhere in the Indian Ocean region. from Africa to South-East Asia and everything in Between.
From certain Locations using payloads , even Europe can be reached.
Really speaking , the need for Long range ICMB's beyond a range of 8000km(Which i am guessing what What the next Agni missile maybe) does not exist.
When IN feels it can venture into the Pacific and Atlantic.(Can only happen after it has consolidated its assets in the IOR)
IAF expresses the need for Long range Strategic Bomber.
And IA expressed the need for more Marine Landing ships and Long range Lift aircraft.
We should then look to expanding the range of our missiles.
Other wise there is no reason to accelerate the process for more long range , as we make improvements to the Agni Missiles , range will also increase. We could attain longer range missiles like that.
But actively spending on R&D to make longer range missiles , that cost more and are more expensive to make and have no clear target . Is a waste of energy , focusing on better accuracy , MIRV , portability and EW capabilities of our Missiles is more important