He could be anything from a guy who never gets out of high A ball to the next Chase Utley. It's all projection and speculation at this point. It's fun to do but ultimately meaningless
This is why I cannot fathom why people get so up in arms when you disagree with them over what you think a prospect will ultimately be. If you think Shewmake is going to be a top notch starter, that's great. I hope you're right. If you think he's going to bust out quickly, that's certainly your opinion. Even the guys who do this professionally are wrong about what players will become a huge percentage of the time.