Version 602 of Roassal.mcz and Trachel-AlexandreBergel.239 addresses the bug with RTPolygon.
For RTEllipse, I am not sure how to fix that...

It is possible to draw an ellipse with a uniform scaled stroke (with cairo).
Athens just don't expose this api. (there was a lenghtly discussion with no result
http://forum.world.st/Athens-and-ellipse-drawing-tt4754256.html#a4765659)
Here is an example for an ellipse with uniform stroke.

    | view |
    view := AthensSceneView new.
    view
        scene: [ :canvas | 
            | stroke ellipse |
            canvas surface clear: Color black.
            canvas pathTransform
                restoreAfter: [ 
                    canvas pathTransform scaleBy: 1 @ 2.
                    ellipse := canvas
                        createPath: [ :builder | 
                            builder
                                absolute;
                                moveTo: 10 @ 75;
                                ccwArcTo: 75 @ 140 angle: 90 degreesToRadians;
                                ccwArcTo: 140 @ 75 angle: 90 degreesToRadians;
                                ccwArcTo: 75 @ 10 angle: 90 degreesToRadians;
                                ccwArcTo: 10 @ 75 angle: 90 degreesToRadians ].
                    canvas setPaint: Color blue.
                    canvas setShape: ellipse.
                    canvas draw.
                    stroke := canvas setStrokePaint: Color red.
                    stroke width: 8.
                    "---------------- all the following uses athens-cairos PRIVATE api --------------"
                    "load the path with the current active (scaled) matrix"
                    canvas newPath.
                    canvas loadPath: ellipse ].
            "explicit set the (restored/identity) pathMatrix"
            canvas setPathMatrix.   
            "dont call draw it would again load the path with the now active pathtransform" 
            "just load the color and render the stroke"
            stroke prepareForDrawingOn: canvas.
            canvas stroke ].
    view openInWindow.

borderWidth/borderColor works for polygon shapes, but RTPolygon does not initializes
the stroke property therefore, methos like examplePolygons throws a MNU:
MessageNotUnderstood: receiver of ""asAthensPaintOn:"" is nil

Is this still an issue?

yes, RTPolygon can not be used without explicitly setting the border color.
(can I get right access to the roassal repository)

For drawing ellipse with a uniform border width we need a change in athens drawing
api.
(we should discuss this on pharo-dev)

As per the linked thread, you can do it with the athens drawing API already..

ellipsisOfExtent := [:builder :anExtent | | halfX halfY | 
            halfX := anExtent x / 2. 
                halfY := anExtent y / 2. 
                "We expect relative builder, and start the ellipsis at anExtent x /
2 @ 0" 
                builder 
                        curveVia: 0@(halfY negated * 0.55) and: (0.45 * halfX)@halfY
negated to: halfX@ halfY negated; 
                        curveVia: halfX* 0.55 @ 0 and: halfX@ (0.45 * halfY) to: halfX
@ halfY; 
                        curveVia: 0 @ (halfY * 0.55 ) and: (0.45 * halfX negated @
halfY) to: halfX negated @ halfY; 
                        curveVia: (halfX negated * 0.55) @ 0 and: halfX negated @ (halfY
negated * 0.45) to: halfX negated @ halfY negated; 
                        close]. 

AthensSceneView new 
        scene: [ :can | 
                | path | 

        path := can 
                                createPath: [ :builder | 
                                        builder moveTo: 10@60. 
                                        ellipsisOfExtent value: builder value: 200@100
]. 
        (can setPaint: Color blue;
            drawShape: path;
                setStrokePaint: Color red) 
                width: 8 asFloat. 
        can drawShape:  path ] ; 
        openInWindow 

What is indeed impossible in Athens, is drawing unscaled strokes on a scaled path, since
path scaling only occurs as part of drawing, not creation.

The above avoids that by using no scaling to draw the ellipse.

Ah thank you,
I thought this kind of "ellipsis" wouldn't be like a real ellipse and would look different,
but it looks quite similar (can not see any a difference).
We should take this solution.

I attached a changeset with the above mentioned ellipse drawing.
And Polygonshapes with no border are working again.

I moved the strokeWidth, and accessors and the method drawStrokeIfNecessaryOn:
up to the TRShape class