Would be great if this app could be placed in the system tray, and since this is a wishlist item, maybe the icon could show temp with a background of cloudy, sunny, rain, etc. as other weather apps have done in the past, but having it in the system tray and clickable would be an excellent start. Unless I'm missing something (which is entirely possible) there doesn't seem to be a comprehensive weather app such as kweather for the system tray. Yes, there Weather Report widget, but compared to kweather it is quite spartan. Then there is the Event Calendar plasmoid (which has a weather function) which isn't an official KDE sponsored app, which seems to have fallen into disrepair and no longer actively maintained.
By system tray, do you mean as a Plasma plasmoid? That could be interesting, while there does exist a plasmoid, it is more meant for the desktop background.