Missing functionality for writing powerful QtQuick apps

We've seen extensive use of Kirigami for KDE's small to medium sized apps and System Settings KCMs, but we haven't really seen much adoption for the biggest and most powerful apps. Merkuro and maybe Haruna are some counter-examples, but they're the exceptions, not the rule.

There are many reasons for this, but I think one of them is missing functionality that powerful apps want, compared to QtWidgets. Let's collect examples in one place here:

• Customizable toolbars (i.e. the thing provided by Kxmlgui): libraries/kirigami-addons!75
• Dockable panels (i.e. a QML equivalent to QDockWidget)
• Configurable keyboard shortcuts without having to pull in Kxmlgui for its configuration window
• Standard keyboard shortcuts in QML: kconfig#8
• Standard GUI actions in QML: kconfigwidgets#8
• Standard method to save and restore window sizes and positions in QML: kconfig#9 (closed)
• Standard file view (i.e. the thing provided by KDirOperator in KIO)
• Named pixelmetric units that are easy to use: #74 (comment 947818)

There may be more; feel free to add them.