Desktop icons are one of the most basic templates for Activities. Presumably, the template is intended for those who want to maintain different sets of icons for different tasks.
The problem is, KDE itself recognizes only one Desktop folder. While you can easily create a separate folder for the icons used by a particular Activity, all the icons will have a .desktop extension added to them. Although the extension doesn't interfere with the purpose, it's unnecessary and annoying.
The last time I wrote about Activities, one commenter suggested that you should be able to associate Activities with networks and remote desktops.
Another comment from the last time I covered Activities was that they didn't go far enough in their independence. Yes, you can change the background wallpaper and the launchers (if any) for each Activity.
But why stop there? Why shouldn't each Activity be able to have its own customized panels? Or maybe on one Activity where you do serious work, you don't want to be distracted by having notifications display. On another Activity, you might want an extra panel because you always have a lot of windows open. Activities have already moved a long way from the single desktop metaphor, so why not take them to their logical conclusion?
Unlike virtual workspaces, Activities are configured in the horizontally scrolling window that is also used to move between them. This is a cramped space, with small icons that are easy to miss unless you are careful.
Moving Activities to System Setting would make the existing settings easier to change. The move would also give more space for options, so that you could, for example, set up five Activities at once, naming them and adjusting the number of virtual workspaces for each in a matter of seconds, rather than handcrafting each Activity separately as now.
In addition, the move would make Activities easier to find -- which might just people more likely to use them. As things are, Activities remains an afterthought on the desktop that is too easy to overlook.
Probably, someone is likely to suggest that, if I want such improvements, I should code them myself. However, I make no claim to coding skills, while I do have some background in testing and usability. Just as importantly, I have enough familiarity with Activities to understand how useful they are, and how much more useful they could become.
At any rate, many of the changes I've suggested are either minimal or a matter of organization rather than writing completely new code. It seems to me that KDE's Activities are about eighty-five percent of what they should be, and that relatively little effort would be needed by those who know them best to improve them out of all recognition.
A few improvements, and KDE's Activities could finally be seen for the innovations that they are, instead of being a curio at the edge of most users' awareness.