Before Rafael Nadal came on to the scene, the only time players really changed their follow-through, was because their opponent had struck a very deep, aggressive ball to their forehand, and in return, the only follow-through would be a high one, resulting over the right shoulder. One thing that people say about Nadal is that he hits the heaviest ball of all-time, especially off the forehand side. One way he generates this impressive amount of topspin, is from his same-side follow-through that he uses not only falling backwards, like most people before him, but also coming inside the court. One difference between this follow-through, and the one previously mentioned, is that if you watch Nadals' swing in slow-motion, you will actually see that most the time he extends all the way out in front of him with his left arm, and then comes up over his head, finished over his left shoulder. By doing so, he gets a tremendous amount of brush on the ball, resulting in more topspin off the forehand than anyone in the history of the game.
If you ask me, I believe that in the coming years, more and more players will ask themselves, "how can I hit a heavier ball?" and one clear answer, will be to implement the high follow-through. With that said, I believe that in the next decade, more and more top players will hit the ball with the same type of swing like Nadal does.
Try the high follow-through, and I'm sure that it will help you get more topspin on your forehand