1

Create plasmoid with configuration dialog to select KWin effect to toggle it on/off. The effect will be activated/disabled once user click on plasmoid (this plasmoid could acts like button/toggle button).

Additionally, in config dialog, user may select similar additional condition to turn effect on like in spectacle, so wait some time after click, activate effect on additional mouse click, etc.

I think, you could also implement right click on plasmoid, so menu with options of additional activate conditions would appear, but after selecting from menu, selection won't be saved, but it would be associated with next activation.

Why? For example to put very useful effects on panel, like window preview (desktop grid?), magnitude, etc. User don't have to remember keyboard shortcut, but activate/deactivate KWin effect on panel.