It is rather not QML vs Electron but QML vs DOM/WebGL.
We were using QML to create Flowbox (http://flowbox.io). The amount of performance problems when rendering complex shapes and updating the QML model was so big, we would never choose QML for something like Luna. Moreover, there are a lot of performance bugs that are unable to be resolved in QML (Flowbox team was trying to resolve them together with Qt team, but without success - the conclusion was that the current QML design makes it impossible to express some dependencies and it will probably be fixed in the future).
Moreover, Luna should be runnable in web browser, so QT is no option here.
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