There are two packages specifically for PreTeXt that can speed up writing. First, language-pretext 2  provides syntax highlighting and snippets for PreTeXt documents. This should highlight math enclosed in <m> tags and in fact allow you to use snippets there. The PreTeXt snippets allow you to, for example, start typing example and upon hitting return or tab, expand to the tags needed to write an example. Particularly helpful are the snippets for <p>, <li>, and <m>, as these put your cursor in the right spot (hitting tab again should pop you out of the <m> tags).
atom.io
atom.io/packages/language-pretext
atom.io/packages/linter-spell-pretext