Ever since GNOME 3 received support for extensions, I've been using this one:
https://extensions.gnome.org/extension/302/windowoverlay-icons/

It is usually among the top of 'must-have' extensions lists everywhere you look.

I'd like to request to move it into GNOME core. It makes window switching much easier, because you can easily see which window belongs to which application. Without the icons, many windows are just white rectangles with thin chrome, which hardly distinguishable from the overview. For example, it's almost impossible to distinguish windows of different web browsers - the only thing you see in the preview is the content, but you can't easily tell which of those windows is Firefox, Chrome, or Epiphany.

The same problem occurs with e.g. editors with an empty document opened - you see only a white rectangle. If you happen to have an empty gedit opened and a blank page in Firefox, you can't really say which window is gedit and which is Firefox, all of them are simply empty and white.

Putting application icon somewhere, either as an overlay into one of the window corners, or next to the text description, vastly improves the speed with which you can recognize the right window and switch to it.

I believe large and recognizable application icons in the overview are consistent with the rest of the gnome-shell interface. GNOME 3 made the app icons in the alt+tab switcher much larger (a change which I greatly appreciated). There is a medium sized icon of the currently focused app in the top bar, and there are big icons of the favorite apps in the dash. GNOME 3 clearly support the use of large and recognizable icons for identifying switching between apps. It also supports displaying window previews (the overview mode). The missing piece is tying those two parts together. At the moment, we have the icons and we have the window previews, but it's not always clear which window is which application, and which application embodies which windows.

Placing an app icon over or next to the window preview would make it navigation much easier and more pleasant.

Thank you.