As a future upgrade, I would love to see independent post boost vehicles for each RV like the Yars-M (so even in early midcourse, destroying one MIRV bus doesn't destroy all RVs) and extendable nozzle cones, if it hasn't been employed already.
The Agni-V Mk2 (Divyastra) is an advanced, MIRV capable iteration of the Agni-V.
Major improvements include replacement of maraging steel first stage casing with one manufactured using carbon composite filament winding, it is India's largest composite casing for now.