Million dollar question, our FM didn’t reduce in this year budget. Hopefully something happens in the next years. Personally doubt if this can be reduced considering India’s fiscal deficit.
This STT is laid by Government/NSE and so most probably will not get reduced.
Lets hope it will not increase in future years. 
Note: Zerodha is only taking Brokerage charges, other charges are mandatory and laid by NSE/Government only.