This is a wishlist feature, but as a general workaround to an actual bug #340120 and other issues like it.

Some laptop docks,  such as Dell's, seem to cause a short delay in reporting the properties of attached displays. I've verified the existence of the delay by immediately after login getting xrandr information which turned out incorrect. After a few seconds the information updates with the correct values.

This causes the displays and resolutions shown on the KCM be incorrect (for example only having one resolution option). Because of this setting up the displays isn't always possible using the KCM and xrandr must be used directly instead.

I propose a button or some other means of forcibly refreshing the display information on the KCM. Always reloading them on entering the KCM would also be enough.

Reproducible: Sometimes

Steps to Reproduce:
I'm not certain on the specific circumstances because it seems highly hardware-dependant, but this is the setup the problem manifests for me with:

1. Get a Dell Latitude e7440 and the associated dock
2. Connect two displayport displays to the dock
3. Power on computer, log in to plasma desktop
4. Go to kscreen
5. The DP-displays are shown with only one resolution
6. xrandr shows correct display information (a few seconds after login)

Actual Results:  
Incorrect display information on kscreen KCM.

Expected Results:  
The information should either update when the dock changes the properties or allow manual updating.