Tons of helpful feedback here. Thank you!
Several people asked why we removed support for multiple instances. Rest assured, we had no desire to do so. To release Power BI Report Server every few months, independently of SQL Server, we needed to develop a new installer separate from the SQL Server installer. (There was other customer feedback that called for a separate installer as well.) There’s simply more work for us to do to reintroduce multi-instance support within this new installer. We don’t yet have a timeframe to share, but yes, we do plan to reintroduce multi-instance support!Riccardo Muti commented
@Ian, you can run multiple instances of Power BI Report Server on the same physical server today through virtualization at the OS/VM level, just not through a "multi-instance" feature built into Power BI Report Server. This shouldn't be a licensing issue, more of a manageability issue.