I didn't know that it is thought to be a Stevie original
I don't know why, but I always thought that it might be an old country song or something that her grandfather sang and/or wrote. Anyway, you are right, it's very short, but then again, so was Secret Love, and that got fleshed out. But you are also right that maybe a secret cut at the end would be a great place for it.
Here's hoping...
Kevin