I think they will regret switching to QML. It isn't nearly as robust as QtWidgets and doesn't scale to large apps like this very well (I'm not actually aware of any large apps that use QML).
If it were me I would wait until Qt 6 is released. The Qt developers are making some changes to QML that sound like they have learned at least some lessons (e.g. adding strong typing, not relying on Javascript).
If it were me I would wait until Qt 6 is released. The Qt developers are making some changes to QML that sound like they have learned at least some lessons (e.g. adding strong typing, not relying on Javascript).