However, I wonder if the multi-nationals and banks in HK would feel comfortable with economic control being handed-over to Beijing and with a distanced administration in either Guangdong or Shenzen?

Will be interesting to see how that one plays out. But given how the chinese have kicked facebook and google out of China, despite Zuckerberg fawning to the Chinese president in Chinese, I honestly think that the Chinese won't give a s**t. It will either be a like it or lump it scenario, they have HK by the balls now, for better or worse.