I assume the requirement is waived for Stat PhD programs. I think only Stanford had it as a requirement before, and the Subject test was used as a screening tool (so anyone who scored under [x] percentile was not seriously considered for their program). In my opinion, it should not be required to begin with for Stat programs, since it tests things like abstract algebra, number theory, topology, etc. that have little relevance to statistics. But clearly, some elite PhD programs feel differently.
I assume that Stanford and other schools that "strongly encouraged" the subject test will just weigh the other factors more heavily -- GPA, grades in upper division math classes, class rank, letters of recommendation, reputation of undergrad institution, research experience, general GRE, etc.
Only a few top schools recommend/require the test. If the test is cancelled due to the pandemic, I guess they will waive the requirement so I wouldn't worry about it.
