I apologize for cross-posting; I'm trying to reach all projects here, and encourage you to translate and spread this message to relevant village pumps. (I explain a tool here, some points, and provide you with a link where you can participate in the discussion I opened.)
The WMF Engineering Team is kindly working on Media Viewer, which would show a pop-up of some sort when you click an image. This tool is available for testing to those people who created an account, in Beta tab, on all projects. Like you may see the tool has a relatively high impact on average reader experience.
It came to my mind that the tool goes full-screen, which doesn't meet the "I stay on the article" expectation. I feel it may be important to an average reader to gain orientation.
I opened a discussion, with some people calling my idea a "metadata pop-up" rather than a "media viewer". I feel that may be good thing: the existing default opens a lot of image info and tells people what Commons is. I feel the media viewer should do something close to the same, with the advantage of not leaving the page, and some interactive means of viewing the image if the user clicks some buttons.
As opposed to that, a "Media Viewer" would show a bigger image and make use of space. But the mock I have is slightly bigger already, like the existing "File:*" page. I am not assuming that the reader wants a bigger image; I'm assuming he may also be interested (and it would be more transparent to) in reading some metadata, description, date, author.
Please see the discussion here and weigh in, basing on your preferences and Wikimedia projects experience. Your voice powers the future of the tool, and Wikimedia projects.