There is no constitutional requirement as to the number of justices.
We started with 6. The number fluctuated over the years, rising to as many as 10 and finally settling at 9.
Maybe we should set the number back to 7 and let attrition take the number down.
Maybe we should wait until a true conservative take charge in the White House and raise the number to 11.
IMHO the Constitution should be amended to provide that a justice be selected (at least on average) every two years, and justices retire as necessary to maintain 11 justices on the bench. I am agnostic about the role of presidential candidates in nominating justices, but consideration should be given to electing justices in off-year elections.To me the ideal constitutional amendment would be created by convention, and would explicitly name the justices of SCOTUS. Which would assert state supremacy, of a sort, over SCOTUS since it would not require any action by Congress or the president.