Mo but being underwater for long time in enemy territory and in conflict firing brahmos in salvo mode on carrier battlegroup , imagine 50, 60 brahmos approaching your fleet of 20 ships .
Two ssn escorting it can take care of rest of submarine fleet .
Its a good idea but you need to absolutely certain that those ships will get hit and destroyed with your missiles. Because if the enemy retaliates, you lose a very priced asset that costs more than Destroyers. Along with them, you put the SSN escorting it on risk.
This certainly can't be attempted in enemy territory (South China Sea) where even if you take out the fleet, they'll have drones or jets or ASW aircraft on top of you from land bases. Not to mention the entire trio of SSN and SSBN could get tracked all the way in to the South China Sea with passive sensors like a SOSUS hydrophone array. Not to mention the number of Chinese submarines in SCS alone will outnumber our submarine fleet.
A better idea is to hit them in the Indian Ocean when they are maneuvering towards the Indian Surface fleet. When the PLAN fleet crosses the Lombok or Sunda straits and come for us (during a war), we can have such a fleet of SSGN and SSN waiting in quiet mode South of these straits. When the PLAN fleet starts moving North towards Indian subcontinent and the waiting Indian surface fleet, the SSGN and SSN could follow them. Most of their ASW effort would be directed towards the front and flanks, making their aft slightly more vulnerable.
But for this to happen, SSGN should be capable of keeping up with the enemy fleet. An SSBN converted to SSGN role will likely not be fast enough. Maybe we could create a dedicated SSGN class with S4's body and the new S5 class's reactor? That would definitely be capable enough.