I do not know for a fact, but I suspect that many mainland PSBs are closely scrutinizing Hong Kong generated Z visas. It is no secret that HK has seen visa-generation process as a profit making enterprise for local agents. And HK-Mainland relations are, shall we say, currently stressed.

It may seem like a secret so well kept that they the Hong Kongers don't know about yet; the trickle of bums with rucksacks and sod all cash to spend won't impact the Hong Kong GDP very much I think. You suggest it may be the straw that breaks the camels back as far as HK and mainland relationships. Don't see how, Hong Kong won't miss the bums and China doesn't have to accept the resulting visas when and after they return and claim RP.