Here's a quick first draft of a mobile article preview gadget:
https://meta.wikimedia.org/wiki/User:Brion_VIBBER/mobile-sidebar.js

This shows the currently viewed page on the mobile view in an <iframe> sidebar, and captures link navigation within the iframe to navigate on the desktop window as well.


To enable add to your ~/common.js:
mw.loader.load('https://meta.wikimedia.org/w/index.php?action=raw&title=User:Brion_VIBBER/mobile-sidebar.js&ctype=text/javascript');


Todo:
* add an on/off switch
* fix width to adjust for scroll bar if visible
* make a couple common sizes selectable instead of just 320x480?
* figure out how to apply this to edit previews? (is this even feasible without API changes?)
* fix edge cases with the navigation detection
* pretty it up
* enable as a gadget on some major sites

-- brion