Like the SSRS, Qlik, and Tableau; Power BI reports should cover the entire page to display it's visuals. Currently, user get to see the reports in Power BI Report Server or Service in a canvas. And make the power bi reports responsive so it will adjust it visual according the screen size.
This feature already available when design the mobile reports from Mobile Publisher in Report Server. I believe it should not be very complex to incorporate in existing environment.