I noticed that the reference implementation allows alternate calling form of vector-accumulator,
reverse-vector-accumulator and bytevector-accumulator, e.g.
(vector-accumulator n fill).
Is it intended to be in the spec?

I feel that such use case is easily covered by vector-accumulator!, e.g.
(vector-accumulator! (make-vector n fill) 0).
However, in that case, we might want reverse-vector-accumulator! and bytevector-accumulator! as well.