Instead of crying over spilled milk, I would suggest that we start to think about damage control now an estimated 600,000 candidates are eligible to come to the SAR following the Court of Final Appeal's ruling on the right of abode issue.
The best way to start is look at how the United States government handles the mammoth problem of literally thousands of people crashing at the gate to America, no doubt the most sought-after country by immigrants. Under the doctrine of plenary power, the US government enjoys sole and full authority over the local regime governing immigration, and the actions of the political branch merit extraordinary judicial deference. By analogy, the SAR Government (headed by the Chief Executive) should have the ultimate power to decide on immigration matters, that is, within the law.
The US Immigration Act of 1990, which is the current law, establishes an annual limit for worldwide immigration, under which certain quotas are assigned to three categories of visa for entry to the US, family-sponsored immigrants being one. Visas (entry permits) are granted on a first-come-first-served basis. Because of the quota control, immigrants learn they may wait years before applications are granted.
For family-sponsored immigrants (comparable to 'right of abode' cases), the system prioritises applicants according to so-called 'preferences'. 'First preference' is allocated to 'unmarried adult sons and daughters of US citizens'. For each preference, there is an annual quota. The SAR could do the same; the control is legitimate and in keeping with its autonomous status under the Basic Law.
Each application for entry to the US under the first preference must include proof of a 'bona fide parent-child relationship'. Documents such as money order receipts that show the father's financial support of the child, income returns that show the child as a dependent, and so on, must be produced. The SAR could consider, in addition to these, a DNA test to establish a bona fide parent-child relationship for each applicant.
Another feature to be considered by the SAR is the so-called double-check system used by the US.