I wonder if it would simply be easier to go right to the antibody test, especially since we know the PCR viral test is not particularly sensitive, meaning people with low, but non-zero viral loads will still be donating, even if they have negative viral tests
Absolutely, great points. Still much we don't know about antibody levels and neutralizing antibodies (and memory B cells and more), including are our tests discriminatory enough and even if they are, do we know how much of which component is key to immunity and for who long and in which patients, etc., etc.. The Scientific American article provides an easier to read, but still pretty insightful, overview of many of the issues and the 2nd one has a deeper take on the science.
That's why I'm simply so curious to see the results of the trials of the plasma therapy, i.e., can we at least confirm remission of very serious viral infections, as was seen in the two small Chinese studies (with 5 and 10 seriously ill patients, including on ventilators)? If that is confirmed and that's all it does (i.e., even if it doesn't confer long term immunity), even that is huge and scalable for 10,000 seriously ill patients in the US. If it's much more effective early in the infection, then scalability would be more difficult with obviously many more patients.
https://www.scientificamerican.com/article/what-immunity-to-covid-19-really-means/
https://onlinelibrary.wiley.com/doi/epdf/10.1111/vox.12926