I started looking at this. It's annoying because the code to do the wikitext detection is already there and working for the main surface. It would be trivial to do the absolutely wrong way (i.e. copy the existing code to the reference surface or image caption surface and just change the reference to the Surface object), but it's a pain to fix the proper way.

One of the problems lies in the differences between normal surfaces (i.e. the main one) and surface widgets. It was suggested that we could implement MWSurfaceWidget which does the wikitext warning, but the main surface is not a widget and would still need it's own version of the code.

Also, we can't just shove the wikitext detection code in the ve.ui.Surface class and guard it with some config, because the Surface code lives in VE core which does not deal with MediaWiki features (wikitext) - the VE MediaWiki extension deals with that.

Roan suggested we could make the main surface be a surface widget and then create an MWSurfaceWidget, but that apparently has issues involving toolbar floating (I'm not familiar with this, perhaps it could be fixed in some way).

I think that for now, we can probably change the wikitext detection function to accept a surface parameter, then make it static somewhere and have each wikitext-free surface to set up an event handler for it.

Change 138761 had a related patch set uploaded by Alex Monk:
Show wikitext warnings in the reference dialog

https://gerrit.wikimedia.org/r/138761

Change 138761 merged by jenkins-bot:
Show wikitext warnings in the reference and media caption dialogs

https://gerrit.wikimedia.org/r/138761