That comment was actually already there, I just moved it down to the new method when I split out the code that creates datastreams ( https://github.com/UNC-Libraries/Carolina-Digital-Repository/pull/120/files#diff-be9af99ba7fbea5a047b2b25abd599e7L153 ).  But yeah, it'd be good to be able to include arbitrary RDF properties on datastreams in the future, such as the metadata profile.