This is a fundamental workflow feature on the Exposé/Mission Control implementation of this kind of effect on macOS since _2003_. I think the rewrite of Present Windows is a good time to bring this to mind: You should be able to drag files, initiate Present Windows, and drop the files on a window there. Since this reimplementation of this effect in Plasma 5.25, the drag & drop part for the first time somehow works in Kwin, even with screen edges. But it doesn’t drop the files in the right window… It drops them in the window in the exact position your mouse cursor is without Present Windows on.

How this should work: You drag a file and initiate Present Windows to drop it to another window there. The hovering above a window should be animated somehow to express that you are about to drop a file there. When you actually drop it, it should fall into the window.