User blog comment:DaNASCAT/Technical Update: September 28, 2015/@comment-24473195-20150928213236

As far as link previews are concerned I think the newer version of Wikimedia's VisualEditor has wikia beat. First they show previews of images related to the article and this helps determine if its the right one to use.

Secondly, it automatically changes an "external link" to an internal one, so for example, if one pastes the following:

https://www.mediawiki.org/wiki/Help:VisualEditor/User_guide#Editing_links

The visualeditor automatically parses that link and converts it to something like mw:Help:VisualEditor/User_guide. It also seems to do the same thing for interwiki/interlang links, which helps if one pastes a wrong link.

My suggestion is that wikia implements something like that. The images have a bandwith cost, but parsing the link and detecting local links is quite easy to write, even a simple lua module can do it (see Wikipedia:Module:Interwiki).