SML/NJ, as I understand it, is implementing Successor ML features, so one of three things is true:

(1) Successor ML is happening,

(2) Standard ML is alive and evolving,

(3) SML/NJ isn’t just an implementation but a distinct language which is a successor to Standard ML and which incorporates what was described as “Successor ML”.

Yup. Realistically, the successor of ML is in fact OCaml.