User blog comment:DaNASCAT/Technical Update: October 21, 2015/@comment-1251315-20151021200442/@comment-126761-20151023095846

In case of newer comments above not being noticed: the user preference about syntax highlighting will cover template pages as well (and in fact in planned to expand to cover CSS/JS pages). The simple classic editor isn't going away.

The 'convert to infobox' notice isn't really related to the highlighting change, though.