If ZERODHA is very serious about their services, I strongly recommend them to talk to MT4 guys.
MT4 is trading terminal used by many forex brokers like OCTAFX. Its super fast and truly international as it is stable now and used by many top notch companies.
Else they may contact many other companies who offer their own softwares.
Zerodha guys can also see GCI MT4 terminal , they are offering Reliance, Airtel, Tatamotors, Infosys etc shares for trading.
So I cant see any reason why it cant be customized for Indian stock market needs. One can download it from here
http://www.gcitrading.com/mtdemo.htm and open a demo account from with in the terminal itself and check.
I heartily wish MT4 to be used by indian stock brokers one day.