Before we start, we need to understand why Lee Kuan Yew said that in the first place. I would think that the reason behind his statement is that majority of the population is Singapore is Chinese, therefore if we would have a non-Chinese minister, there would surely be some unhappiness in the Chinese community. I do not think that that is the case.
Firstly, I think that the people in Singapore had already gone through a lot since independence, and I believe that the different races have all come to accept and understand each other, and even though there may be some racial conflict, all of us are Singaporean down in our hearts. Thus, even if there is a non-Chinese Prime Minister, I would think that the majority of Singaporeans would come to accept and embrace it.
Secondly, if we were to have a non-Chinese Prime Minister, it would be good to the image of the government. Having a non-Chinese Prime Minister would show that the Singapore Government embraces racial harmony, and this would further promote racial harmony in Singapore.
Lastly, I think that a non-Chinese Prime Minister might even be beneficial to the PAP's votes and cause the votes to increase. This is shown by the fact that President Obama won the hearts of people all around the world by being the first black president. If there would be a non-Chinese PM in Singapore for the first time, people in Singapore might even side to the PAP.
Adios for now :)