Oh hey. Didn't see you were still stuck.
So if you've QML declared your (LineSeries, ScatterSeries, and SplineSeries) - in C++ you'd have a slot (or Q_INVOKABLE) receive the object as a QXYSeries* ptr.
Once you have access to a QXYSeries object: (you have a pointer to your series and you know which c++ std::vector matches what series etc) the only work you have to do is reformat your std::vector into a QVector<QPointF> before the replace() call of the QLineSeries*
The LineSeries will do the work to repaint.
I guess it signals: void QXYSeries::pointsReplaced() which kicks of some ChartView dirty or repaint request. Anyhow, it's free to us.
