It will be the biggest failure of the Kohli era if India lets the colossal talent of KL Rahul go to waste. He is by far the best batting talent to come out of Asia since the Indian captain himself.
He has the complete game to dominate in all formats and is technically as good as it gets. However, his head is not in a good place at the moment, and the uncertainty over his position/role in the team has dented his confidence and unsettled him.
He would walk into most teams as an opener, but in Dhawan and Rohit, India have the best LOI opening in pair in the world. However, Vijay is on his last legs and KL Rahul needs to be given a long run in the Test format. He may not have done well in South Africa, but he will definitely come good if persisted with.
In Limited Overs, the only place for him is number four for now. The Dhawan and Rohit combination will be there for another 3-4 years, and he is certainly a better long-term investment at number four than Rahane.
However, it appears that the Indian management does not know what to do with him and with the likes of Gill and a few other players making a name for himself, it is likely that he might be lost in the system, which will be a big tragedy for Indian cricket.