Everything KDE from current git master on Wayland with a touchscreen. *Clicking* on a parent category item in the sidebar shows the subcategory page and loads its first KCM. However *tapping* the same item with a touchscreen does not show the subcategory page. The correct KCM is loaded, and the subcategory page is pushed onto the stack. However it is not automatically shown. Likely related, or with the same root cause: if you manually swipe to the subcategory page and tap the back button, it visually depresses but does not take yo back to the base page in the page stack.
The call to root.pageStack.push(subCategoryColumn); seems to be acting differently with click vs tap, for some reason.
*** Bug 439924 has been marked as a duplicate of this bug. ***
Hmm, this is working for me now on X11. Will re-test with Wayland.
Working on Wayland too now for me. I guess this god fixed in some other part of the stack.