Hey, Jason. Thanks for reaching out!

The changing element, was a crude example. There will be situations where you do change element though - say from an <ul> to an <ol>, or from a <section> to <main> when you rethink the content and what it should mean.

I think the class names used throughout the article can be ignored in reality, they are just there to get a point across.

However having a unique parent class does not make it portable in the way you have described. Largely due to when you want to nest blocks of reusable code.

.mainMenu {
  em {
    font-weight: bold;
  }
}
.header {
  em {
    color: red;
  }
}
<div class="header">
  <em>Lorem ipsum</em>
  <div class="mainMenu">
    <em>Dolor sit amet</em>
  </div>
</div>

I'm not sure quite what you mean about defeating the point of BEM by using it with SASS, essentially it's just keeping everything tightly knitted and in nice code blocks. It also helps keep down typos when you're not constantly retyping the block name.