Hong Kong needs to stand out among the great cities in its neighborhood. Singapore is fully English-speaking. HK isn't. Shenzhen is fully Mandarin-speaking. HK isn't. But HK can aspire to be both an English- and Mandarin-speaking city.
It would provide a unique advantage if HK could succeed in developing a Mandarin and English school system. It would not only educate its own students, but also attract international students that are interested in mastering both languages.