If I had desktops 2 and 4 occupied and tried to scroll between them I would end up opening 3 while scrolling. In a situation when you have a lot of desktops and only a few of them occupied it would make sense to only scroll through occupied ones. This functionality is supported by bspwm itself and you only need to make small change in the module code for it to work. I have already changed it for myself in a fork but also want to share this. I'll submit pull request shortly after.