I have looked into it earlier, but not keen on it right now for the following reasons:

• We are still on QtLocation 5.2. There is no future in developing plugins for that
• With MapboxGL QML plugin, we have QtLocation 5.9 level functionality. Since it renders maps on device screen directly, you have many advantages when compared to raster-tile based approach. I would expect that most of the map-requiring apps would start using it. However, this QML plugin is non-standard - hence no additional benefit to package the server as plugin for map rendering
• When(if) QtLocation 5.6 will land to SFOS, I may look into it. But note that it has to bring something significant for me as a user as well. If there is no significant gain that we, as users, can see in terms of better apps developed, there is very low motivation in repackaging the working solution

I am currently working on bringing MapboxGL vector tiles to OSM Scout Server. It would take some time to figure out how to convert the maps, but I am making some progress. One of the available solutions uses docker with a rather lengthy planet import into the postgis db, but it looks like I maybe able to avoid it. I'll try to get to the scheme that's compatible with the server setup by @otsaloma