QGCCorePlugin is currently constructed with a QGCToolbox* toolbx parameter of null. This is because at the time QGCCorePlugin (or an actual custom plugin) is constructed app->toolbox() is null.
_scanAndLoadPlugins() is called as part of the QGCToolbox constructor where all toolbox classes use the same format:
_class = new Class(app, this);

The creation of QGCCorePlugin should follow the same pattern.

The practical issue I had with this is that because the parent is not set correctly, QGCCorePlugin is not destructed when the app is closed. This means any code in the destructor is not run. (QGCCorePlugin itself has as a destructor which is currently not being called).

New wizard done model

Drag of land/loiter maintains land distance/heading as appropriate

Fix return value

Out Survey polygons with KML save

Stable update

Add support for chunked STATUSTEXT

Remove unused HIL code

Fix hamburger positioning

Much better mission->kml conversion support

Use global palette

Add support for isTakeoffCommand MissionCommandUIInfo

Fix typo

Add global palette object to QGroundControlQmlGlobal for generic usage

Remove unnecessary includes of QGroundCotrolQmlGlobal.h

 - UVify Core board support is implemented.

Guard against UI Info not available causing crash