Well, it definitely does _something_, because on NFS the subsequent stat() calls after reading the directory names do indeed complete instantly :), at least in my testing.
I mean, readdirplus as a local filesystem API. Ultimately unix programs are just invoking getdents() (or equivalent) + stat() (or statx, whatever). Linux nfsclient probably caches the result of readdirplus for subsequent stat.
Well, it definitely does _something_, because on NFS the subsequent stat() calls after reading the directory names do indeed complete instantly :), at least in my testing.