In a speech about the Elected Presidency, Minister K Shanmugam reminded the audience that our Presidency used to rotate among races. According to this rotation, we should have had the next Malay President in 1993. But we have not had a Malay president since.
We need all races at the apex of government to strengthen and preserve our multiculturalism. This is less likely to happen in an open elected Presidency as people prefer to vote for candidates of their own race. Hence, a Reserved Presidency is necessary.
Read his slides below (hover over slides for controls).