You may be surprised, but I wouldn't really want to change anything. I have been studying it one way way or another for sixty years now, and I love its oddities.
I suppose if I had to change something, I would try to put some consistency in the way we use the definite and indefinite articles. It is one of the few areas of English grammar where the more you learn, the less you really understand. Even as an experienced teacher, I shudder when an advanced student says, "Can you explain why the writer has used these articles here?" (The simple answer is often that I can't.)