We have designs for 4 man crew (Arjun mK1A, Mk2), 3 man crew + manned turret (old FMBT), 3 man crew + unmanned turret (new FMBT) and 2 man crew (new design revealed by DRDO scientists) tanks.
Problem is Army has not firmed its requirements for the last 10 years. Earlier they wanted 3 man crew + manned turret. Then they wanted Armata style (3 man crew + unmanned turret). Now now they want 4 man crew. However weight of all these variants should be in the 40-50 tons. These are purely unrealistic expectations.
I remember back in 2007-08 when Arjun MK1 was getting produced at HVF, Army organized a Future tank conference and invited global speakers to give their input to India's FMBT. There one of the most prominent speakers Maj. General Israel Tal (designer of Merkava tank) spoke that having developed an indegeneous tank, India should work on its upgradation since tank design is an evolutionary phenomenon all around the globe. Nevertheless, his suggestions were ignorned and Army wanted a FMBT and issued hi-fi specifications of its design goal to DRDO. The specifications were not based on its operational doctrice, rather it was a cut-paste job of the specifications from Janes defence magazine of FCS tank (USA) and T-95 tank (Russia) (which at that time were considered future tanks). As usual none of FCS and T-95 materialized in their respective countries.
IMHO they are just stalling the DRDO programme, so that Armata T-14S in the name of FRCV can be brought as a replacement of T-72 and T-90. Army is even tryning to stall the L&T and DRDO JV on 30-35 ton Light tank based on K10 hull; in order to import 2S25 Sprurt SD tank.