If it were possible I would quite like to see Rahane as Test captain and Rohit as white-ball captain, starting as soon in the future as tomorrow, but the cult of Kohli forbiddeth this.
Further into the future, I guess it sort of naturally falls to guys like Shreyas Iyer, Shubman Gill and Prithvi Shaw.
Keeper-captain is a huge workload, and India picking a fast bowling captain in the current day and age seems a little farfetched, so it kind of ends up being a batsman by default. Of those young players, Prithvi Shaw has probably the best captaincy record with eleven wins from eleven U19 ODIs