User blog comment:Kirkburn/Technical Update: October 26, 2015/@comment-24473195-20151027160917

"The special syntax highlighted editor currently used on portable infobox pages will be rolled out to all template pages, to give a consistent user experience. The existing user preference to disable syntax highlighting will turn this off."

I'm glad this was deployed, but I think that in their haste to deploy this, the developers forgot a very simple thing. First time users of the template editor may not know how to add wikilinks, to create file links, to format text, and so forth. Putting someone in a blank editor is like giving someone a puzzle with no instructions and telling them to figure it out. There isn't even a single link to the wikitext help page.

Even experienced editors can sometimes forget the syntax, so the quick toolbar helps. In fact, in my opinion the toolbar should exist in some form or shape  for all code (.js, css, lua) pages.

(That gives me an idea for a JS gadget ...)