I took arbitrary class:
package temp;

import javafx.scene.*;
import javafx.stage.*;
import javafx.scene.paint.*;
import javafx.scene.shape.*;

Stage {
    resizable: false // This line prevent Stage to have right size

    scene: Scene {
        fill: Color.RED
        width: 200
        height: 200
        content: Rectangle {
            x: 0, y: 0
            width: 200
            height: 200
            fill: Color.GREEN
        }
    }
}

And below is the formatting result:
package temp;

import javafx.scene.*;
import javafx.stage.*;
import javafx.scene.paint.*;
import javafx.scene.shape.*;

    Stage {
        resizable: false // This line prevent Stage to have right size

        scene: Scene {
            fill: Color.RED
            width: 200
            height: 200
            content: Rectangle {
                x: 0, y: 0
                width: 200
                height: 200
                fill: Color.GREEN
            }
        }
    }

The first problem is indention: why was 4 spaces added before the Stage class?

I'd like to see this functionality too:
1. Put spaces between mathematical operators (like +, - etc). Example:
(a + b) * 2;

2. Put space after ":" in instance variables initialization. Example:
var bounceImage = ImageView {
    translateX: 140
}

3. Put space  between ":" and variable type. Example:
var springDescription: Text = Text {

4. Don't use several complex instance variables initializations in an one line. Example:
    var springDescription:Text = Text {
        content: "Spring\nInterpolator"
        textAlignment: TextAlignment.CENTER
        *font: Font {size: 16} fill: Color.WHITE*
        x: 10 y: 20
    };