The Standalone Report Designer has a very dated UI. WPF provides so many more capabilities and when you use the Telerik WPF controls, so many possibilities exist.
1. Please put the tool windows in a Docking system, like Teleriks. Forcing the property window to be pinned to the right side is a UI/UX issue. Studies have shown that placing it on the left, makes it easy to use since the object your assign property value is very close and the distance the mouse must be moved it greatly shortened.
2. Make the tool window fonts re-sizable. In the modern age of 4K computer monitors, the very date UI and small fonts make the designer difficult to use.
3. Enable the designer to create assemblies instead of just loose report files. The assembly files can be loose and then compiled as a separate tasks, i.e. shell out and run the appropriate "dotnet" build command to build the assembly. This would enable .NET Core developers form loosing out on many features of the reporting product by being forced to use the standalone designer. For example, Report events.