In training, I get often confronted with a need of STK regarding the Navigation.
On many pages out there, the vertical navigation displays the same pages as the horizontal navigation.
For example when the horizontal provides a dropdown based Navigation, that the displayed drop down level is the same as the starting level of the vertical navigation.

The implementation within STK is, that you cant define a starting level of the vertical navigation. It will always start one level below what the horizontal navigation displays. (line 89 of SiteNavigationModel)
I think the start level of the vertical navigation should be definable.

When trying to solve this problem within the code just for a project, I encountered the problem that I cannot inject a different SiteNavigationModel without using for EVERY stk page template a different STKPageMOdel class, because the STKPAgeModel does a 'new' allocation of the SiteNavigationModel instead of getting it by Components.

Line 88 in STKPageModel

public SiteNavigationModel getNavigation() {
        return new SiteNavigationModel(getDefinition().getNavigation(), getSiteRoot(), content);
    }