My critical issues for an API aree:
1) Node add + custom property values.
2) User add including account abilities and view limitations.
My "nice to have" would be:
1) Node provisioning in NCM, although further integration of NCM with NPM (if licensed for both) would take care of a lot of that, especially if I can provision NCM nodes directly via NPM, or import and add the ssh login credentials.
2) A run of the initial baseline config in NCM after the node is added.
Peter