Would you please explain why did you choose Qt Widgets with Graphics View Framework instead of Qt Quick Scene Graph?
What I would really like to see would be a QRhi-based QPainter implementation for things to be future proof but I understand it's a non-trivial task at all.
Also, even though QML is very nice for projects with more or less fixed UIs, for very dynamic things I find it to be more unwieldy; I reach for it for mobile and embedded without hesitation but for "traditional" authoring desktop apps I'm generally faster to develop with QWidgets/QGraphicsScene in C++.