Is your feature request related to a problem? Please describe.
-r can be used only on CommonJS modules, as documented here. Pre-loading an .mjs or an ESM module package is currently not possible.

Describe the solution you'd like
Either expansion of -r to support ESM modules (might break some people, not sure the scope of those changes) or the inclusion of a --module, -m <module> flag. Neither the long nor short arguments appear to exist in either Node or v8 according to the above docs (correct me if I'm wrong).

Describe alternatives you've considered
None, I perceive this to be a hole in the CLI option set.