To allow creation of dashboards on PBI Report Server. Or, at least, to be able to mix different datasets (data sources) on reports (either PBIX or RDL). I need to use a value from one data source (say, Excel) as a filter on a report that uses SQL as a source. This can be easily done on a dashboard, not on a report.
I'd really like to see dashboard functionality made available in the on premise Power BI Report Server.