As a current Startup School, Europe-based participant [1], this raises an interesting question: if the whole program can be run virtually in a remote-only fashion, then perhaps it can be open for startups from anywhere in the world?
YC-funded startups have never been required to stay in the US after the batch, so it's easy to answer your question. (I've not got any inside information and just found out about this by reading HN like everybody else.)
If the coronavirus pandemic is under control in the U.S. by June, and YC decides to run some of the later parts of the batch (such as Demo Day) offline in SF, that could be a problem for foreign founders who might still be stuck in their own countries or can't get a visa on time. The deadline is drawing near. Without a firm assurance that there will be no location requirement whatsoever at any time, a lot of foreign founders might decide not to take the risk. But YC is not making themselves clear. As I said, there's a huge difference between 99.9% remote and 100% remote.
Anyway, I just saw your more recent comment about over-interpreting the word "may" and I fully agree with what you said there.
I was being a typical reader and reacting to the headline.