Working with generated content from a CMS
It's probable that if you use ECSS with any sort of content management system (Wordpress, Ghost, Drupal et al) you will encounter a situation where it's not possible to add a class to every element. For example, in a Wordpress page or post, it would be unrealistic to expect users entering content to remember the right class to add to each paragraph tag. In these situations, I think pragmatism has to win out.
Set a ECSS class to the enclosing element and (grudgingly) accept that all the nested elements will be set with a type selector. Here's some example markup:
<main class="st-Main">
<h1>How to survive in South Central?</h1>
<p>A place where bustin' a cap is fundamental. </p>
<ul>
<li>Rule number one: get yourself a gun. A nine in yo' ass'll be fine</li>
<li>Rule number two: don't trust nobody.</li>
</ul>
...