Should we always state the obvious? Interface types can only declare methods, properties and events (and assertions, since we're talking about Freya!). Fields, in any case, are not allowed inside an interface declaration.
Properties, however, are designed most of the times to resemble fields. Why should we stick to the property keyword when declaring properties for an interface type?
IScene = interface
Sampler: ISampler; readonly;
Camera: ICamera; readonly;
Root: IShape; readonly;
Lights: Array[ILight]; readonly;
method Render: PixelMap;
method Render(Row, Col: Integer): Pixel;
Of course, if you feel uneasy about dropping the keyword, you can still use it. Notice that there's no possible confusion, even with the declaration of Lights: that's a property returning an array, not an array property.
By the way, the above code fragment shows another omission: that of the final semicolon after the type declaration. Freya syntax has been relaxed to use optional semicolons in several places: after the end keyword in a complex type declaration and after the statement block in a method implementation. We're not going as far as Eiffel, where semicolons are optional almost everywhere, but our new syntax makes easier manual code translation from C# into Freya.