Holy crap they did it! Nautilus FileChooser implementation has been merged!

Nautilus is getting a new file chooser dialog for the GNOME desktop, replacing the current GTK4 file picker, which will also be mobile-friendly.

https://gitlab.gnome.org/GNOME/nautilus/-/merge_requests/1560#note_2f40addfb0ad1052b420879f35b0f76f3de51857

The mockup can be found on GitLab: https://gitlab.gnome.org/Teams/Design/app-mockups/-/blob/master/files/file-chooser/file-chooser.png