Many emigrants sort of made a declaration of Chinese nationality anyway when applying for the Smart ID during their vacation time in HK.

The advantage of a HKSAR passport over the BNO is generally eclipsed by a EU or US/Canada passport, so many who religiously renew their HRP never bothered to apply.

Also, can anyone tell me if a Chinese embassy/consulate will even entertain your HKSAR application? Every time you apply for documents as a Chinese national, they want to verify your legal presence and ensure you haven't been naturalized, e.g. see your green card. A foreign passport certainly conflicts with this policy.