I know it's a bit early to be asking for this, but I wanted to get a feature request on the backlog so it's trackable.
Currently, you already have a ReportViewer for WinUI3. This means you have a good head start for a ReportViewer that can be used in a .NET MAUI project and have native Windows support.
I'm mostly concerned about having support on a Mac, not the mobile platforms. So if you can build a MacCatalyst ReportViewer, you can cover a good portion of developers who are hoping MAUI can give them desktop support across platforms.
Tip: If you use SkiaSharp or Maui.Graphics for rendering, you can get automatic cross-platform support everywhere for free