The closing price for the day of any stock and hence even the index is the weighted average price of the last 30 mins of trading. That is the reason why the last traded price of the day is usually different from the final closing price.
On expiry days towards the close of the market, it is useful for F&O traders if the platform can predict what the actual closing price of the underlying will be. This can help decide on whether to hold on expiring F&O positions or exit them in the market.
Assume that on an expiry day at 3.26pm you have Nifty 17500 calls, and say Nifty is at 17535 and 17000 calls are trading at say Rs 32. Assume at this time the predictive closing price of Nifty is 17525. If you look at the current market price of 17535, you will assume that 17500 calls need to be atleast at Rs 35 and decide not to exit. But if you realize that it will actually close at 17525 which would mean that options will close at Rs 25, you will sell at Rs 32.
We don’t have this feature on Kite. Even when we had this on Pi, it wasn’t really used by anyone. Let me check if we can implement this feature.