Currently we don't translate InsertInto(HiveTableRelation) to DataSource insertion when partitioned table is involved, the reason is that, quote from the comments:
// Inserting into partitioned table is not supported in Parquet/Orc data source (yet).
which doesn't hold any more. Since datasource table dynamic partition insert now supports
dynamic mode (
SPARK-20236). I think it's worthy to translate InsertIntoTable(HiveTableRelation) to datasource table.