Move the units somewhere else
This is something we discussed at the recent sprint.
Kirigami is a bit of an awkward home for Units. They live there for convenience's sake, not because they really have anything to do with a convergent UI toolkit.
I'd like to propose that we deprecate Units in Kirigami and create a better place for them to live during the KF6 lifecycle. Probably a new framework. This new units framework would define units with default values, exposed to both QML and C++, in a plugin-able way so that the values could be overridden by the active QStyle. Then we'd make the QStyle the ultimate source of truth by defining new PixelMetric values that override the ones in the units framework. This way, the active theme would determine the values of the units.
Some units would not need to be overridden at theme level, e.g. icon sizes. They could be defined only in the units framework, and then in KIconLoader, the icon sizes would pull their values from the units framework. And so on.
Anything that had to depend on this units framework would then have to be tier 2, but especially if that was the only dependency, I don't think it would be the end of the world.
@nicolasfella @ahiemstra @carlschwan @mart @nvrwhere @tfella