Marking case with articles

I'm still playing with the grammar one of my older conlangs called Tazhi,
and I was toying with the idea of dropping case endings in favor of marking
case and number with the article.  Here's the idea:

Every noun in the sentence would be preceeded by a definite or indefinite
article.
The noun would remain invariant, and the case and number of the noun would
be indicated by the form of the article.

Suppose that the definite article had the forms:

"da" = nominative singular
"dar" = accusative singular
"des" = dative singular

Then "John gave the book to Mary" would become

"Da John gave dar book des Mary."

And since the case is marked by the article, the word order is irrelevant,
except to emphasize one part of the sentence over another as in "Dar book da
John des Mary gave." = "It was the book that John gave to Mary." (The only
word order requirement is that each article immediately preceed it's
associated noun.)

The form of the article would indicate a plural as well so that if "daren" =
accusitive plural then

"Des Mary da John daren book gave." would be "It was to Mary that John gave
the books."

I might include the option of dropping the article from a singular
nominative and assuming that any noun without an article is the (singular)
subject.

Has anyone seen or used this approach before in any conlang or natlang?

Can you think of any pitfalls waiting for me in this approach?

Thanks, --Gary