> While people in Zhuhai and Foshan and Guangzhou learned a second language so they could talk to their neighbors in Dongguan and Shenzhen and Huizhou, many Hongkongers did not.

I agree with most of your observations, but this part I am afraid is not true. Most of Hongkongers (especially younger generation, no matter what kind of political views they have) has operational proficiency in Mandarin, given that 1. it is taught in school after 1997 and 2. most jobs involves talking to Mainlander/Taiwanese at some point.