I filed in a W-9 form with HSBC, Chong Hing Bank, and probably Citibank HK (it was too many years ago for me to remember). However, this tax residency declaration isn't just for U.S. citizens like the W-9. From my limited experience, it's relatively new.
In conclusion, I've now resigned myself to give my U.S. social security number to any banks I choose to work with. At least my wife only has a US visitor visa, and she can potentially enjoy the benefits of no capital gains taxes, no taxes on interest income, and pretty much only need to pay so little to nothing in HK salaries tax. However, having my U.S. tax filing status as married filing separately (she doesn't actually need to file) has had negative consequences, but the alternative still appears to be worse if not at least significantly more burdensome.
For my son though, in order for him to visit the U.S., he had to get his U.S. citizenship, and with current legislation (subject to change in the next 10+ years that'll matter) he'll have one chance when he's 18 to decide to fairly easily give up his U.S. citizenship or deal with the potential hell of extraterritorial taxes and whatever new annoyances future U.S. politicians create for their citizens living abroad. Maybe he'll study and/or work in the U.S., and in that case being a U.S. citizen is great, but being one abroad is just a real pain.
How many U.S. citizens don't live in the U.S.? Maybe 10 million. How many U.S. citizens live in Wyoming, Vermont, Alaska, North Dakota, South Dakota, Delaware, Rhode Island, Montana, and Maine? Less than 10 million. How many U.S. representatives do all of those states get in Congress? 29! And the ~10 million of us abroad? 0! Life isn't fair.