Hi!
from 2014, so I will research which form is more correct. But for now I would recommend to update the tools to recognize that these literals now may have type. If I discover that the standards or accepted practices recommend otherwise, I'll update further. You can also watch https://phabricator.wikimedia.org/T225996 for final resolution of this.
I surveyed existing practices of SPARQL endpoints and tools, and looks like the accepted practice is to omit the datatypes for such literals even within the context of RDF 1.1. Example: https://issues.apache.org/jira/browse/JENA-1077 I will adjust the code in Blazegraph accordingly, so WDQS will comply with this practice (i.e. result format will be as it was before). This will be implemented in coming days. Sorry again for the disruption.