Additionally, in reality it's not that great a problem - see the UK's connection to the Continent. I guess if the New Territories ever get fully absorbed back into the Mainland, then the border delineation might be tempting to erase and that'll cause problems.
edit: That said, Japan has pulled it off before [2]
[1]: https://en.wikipedia.org/wiki/Rules_of_the_road_in_China#Dri... [2]: https://en.wikipedia.org/wiki/730_(transport)
At this rate, they might as well force all the people in HK to Speak Mandarin, Write in Simplified Chinese. Or get rid of them all together if they don't comply. Oh there is a word for it, Genocide.
The taxis, logistics and trucking industries do have political clout, though, and they will be the ones pushing back.