It would be very handy if we could have a widget showing top x processes using CPU, something like a very limited version of "System Activity". It may only have an option to limit the number of processes (including all processes). I don't think such a widget should also include filtering options (All/System/User/Own Processes or Programs Only) as in System Activity. It may perhaps allow the user to launch System Activity by clicking the widget.
I'm happy to report that this has now been provided by this third party plasmoid: https://www.opendesktop.org/p/2022038
Cool, sounds like the need has been met. :)