Great article as a proof of concept but practically I really don't see the point. I agree that whilst EntityFieldQuery is not a full ORM I fail to agree with the statement:
"There are some approaches in Drupal to facilitate querying data, such as the EntityFieldQuery, but it is so limited that it is barely useful for anything but for making your code a little bit more readable."
EntityFieldQuery has proven quite adequate in my time with Drupal. I would never go to the extreme of introducing Entity Framework in the mix. Especially knowing how slow and tedious .NET development is. (I've been stuck with doing .NET for the past year now) and the extra points of failure in this mix are certainly worth noting.
I would suggest looking into tying something in like Laravel's Eloqent or Doctrine for a more native and sane solution.
Overall though a great proof of concept.