1. It only works from the command line, as it wasn't given a default option.
2. The value of the option is inconsistent with the naming scheme of the other options. Some other names include: indent_start & source_map. This option is sourceMapIncludeSources.
3. The verb embed is probably a clearer verb to use
4. The specs suggest that including the source should be an alternative to referencing the source. Because of this, it shouldn't set the sources attribute for the associated sourcesContent set.
5. It should probably leverage fitzgen's library's option
6. The option doesn't work well with in-source-map.

I'm working on a PR that fixes issues 1-5. The sixth item will be a separate PR.