Hello Zarkopafilis,
After reading over your post I have written a request for the widget screen shake and I have submitted it to the developers for further consideration. I have also provided a link to the public tracker. Please feel free to use the link provided for future updates.
Link: Unreal Engine Issues and Bug Tracker (UE-36131)
As a note: This sort of affect could be created by using the render transform settings on the root of the widget. I hope that this information helps.
Make it a great day