We have been asking for this since 2004 and it is finally a thing. After all of this time, it has a grid view in the file picker in Gnome. After 18 years it is finally a reality. This issue has existed for so long that the original poster of the issue has had children and they are starting college now. Windows `98 had thumbnails in the file picker dialogue and Gnome developers could not add one in 18 years? But this is a very good idea although very late. This is a very famous issue and there are many articles about incompetent Gnome devs and the need for such a simple feature that seemed like it would never be added. I wonder how long it will be until the feature is actually added to Ubuntu and other Linux distributions. Another 18 years? That might happen. Linux needs one very good desktop interface with all useful desktop features like this and other features people expect from a computer desktop and this might bring in more users. But not if it takes 18 years to start on a feature that should have been added in 2007. That is how open-source programmers work.
You are not getting paid to create a feature, so why even hurry? Macintosh OSX machines even have a feature where the user can preview a video in the thumbnail. Plus use a quick preview to watch it before choosing the file. That would be very useful in Gnome. If the useless developers could add this it would be great.