Fully possible and in many ways already done. Design wise its simply adding the star icon to things in get hot new stuff that are considered prime citizens in Plasma (taskmanager, system tray etc). So far so good, after that redesigns would be interesting for some but this is where problems crop up. So far the weather applet is the only one where this is true.

So this is from a design perspective "done" or "wip" but the issue is that it will first off be continous and second need to be implemented in GHNS which is an entirely different matter.