Is there a way to use a FormEditor in an e4 application? I want to migrate an 3.x Eclipse RCP application to e4 and it would be great if there would be a simple way to reuse existing editors.
No you can't use any editor based on the 3.x EditorPart.
I think you can use the org.eclipse.ui.forms plug-in that contains things like FormToolkit, but I have not tried this. The dependencies for this plug-in only contain optional dependencies on 3.x code.