We will not be targeting .NET 5, but are investigating .NET 6
We are actively working on switching to .NET 6 for the Mac version of Rhino 8. We haven’t made a final decision on if this will be done for Windows yet and I’m hoping we can learn a bit more from our Mac experiments before we make any sort of switch on Windows. If we do support .NET 6 on Windows, we would probably also allow for a mode where .NET 4.8 is still used so Rhino can run inside of existing environments like Revit that may still be using .NET 4.8.
All that said, I would recommend plugin devs continue to target .NET 4.8.
WebView2 is installed with Rhino 8 and Eto uses this to provide a modern embedded browser on Windows. We are using WebView 2 for our new code editor which is based on. Monaco Editor