The unhappy Hong Kong citizens can move to countries that although have even much tougher security laws, but also admittedly a few redeeming features that Hong Kong does not have - like affordable housing, as an example.

China will subsequently - and obviously- revoke the Hong Kong citizenship of the departing, using a law that many countries have prohibiting dual citizenship.

Hong Kong will keep those citizens who are proud and happy to remain in Hong Kong, obviously with being part of their motherland, China.

And the UK and Australia will enjoy gaining a new type of fresh, tech savvy, young and modern-minded citizens.

This is a great opportunity for the UK and Australia to replicate the success stories of countries such as USA, Singapore and Australia itself. They also started as emigration destinations for all the wanted and the unwanted, and became powerful and respected nation states, a status that at list most of them enjoy until this very day.

Finally - that's a great deal for Hong Kong and both types of Hongkongers.
Happy? Stay. Unhappy? You are welcome to be happy elsewhere - a privilege that is no longer exist in this anti-immigration world.

A win-win!