I propose that we install gnome-sushi by default.
Sushi is a file previewer for nautilus. It can be activated by pressing the spacebar when a file is selected. Sushi has been a part of core GNOME since GNOME 3.2. It is described in the default user help bundled with GNOME. (The Ubuntu docs are modified to mention that it needs to be installed before using it.)
I proposed this years ago but never finished following up. One change since then is that Sushi no longer uses musicbrainz so there are no dependencies in universe any more.