In Perth, Australia (where Uber has been legalised), taxi plates used to cost around AU$300k, now worth as little as AU$10k. The government is launching an assistance package for taxi drivers in the form of a voluntary plate buy-back scheme that will be industry funded (eg they will impose a surcharge on uber users). Something like this should be workable in HK too.
Buyback schemes are not new to Australians. 20 years ago after the Port Arthur massacre there was a famous gun buy back scheme to rid the county of firearms. The American's could learn from this, and Obama did use this case as an example in a few of his speeches. Too bad the Americans are too stupid to get rid of guns, just like the Hongkies are too stupid to fix their taxi system .