I've had a significant update to Live Preview in the pipeline for a while now. It
brings a few major improvements, the most important of it being able to load
resourceloader modules that the preview requires, fixing a whole slew of problems that the
old implementation had. The only place where it is a bit limited is with regard for
previewing the list of languages in in skins other than vector.
The code is here: https://gerrit.wikimedia.org/r/#/c/131346/
And it could use some user testing and review.
Some people have been asking me about this lately, so I figured time to strip the WIP tag
of it and see if we can get this merged already.
Long term, I would like to improve it to make use of mw.template for some of the elements,
but that is not a necessity right now I think.