I sometimes get sidetracked. I wanted to mention here that we DO have an example of a pure QML maps with overlays example from @cypherpunks in the form of multimodal. It uses Mapbox and doesn’t have any external requirements as far as I can tell (well, api key). EDIT, of course it uses rinigus mapbox plugins 
I package for chum and the map page is here.
harbour-multimodal/MapPage.qml at master · poetaster/harbour-multimodal · GitHub?
It does overlays from the geo coords of public transport stops.
I keep forgetting to post this, but I had wanted to build a ‘minimal’ example app. Which I am going to start, now. EDIT, and of course I didn’t build an example last time because @rinigus has such good documentation