Adopting a GST/VAT would probably seriously alter the streetscape of HK making it a less vibrant city, entrepreneurial city. It would quickly become just another city where mom & pop shops can't compete with the big boys.
Income tax at 50% would eventually mean really cheap housing but given HK's finite land supplies there would be some stickyness in the prices making HK really just too expensive in the short term so would have to move somewhere else.
Maybe North America, ANZ, Northern Europe would be nice for a change