It’s an interesting question, and an interesting ethical debate. But I don’t think we’ll see stem cell augmentation any time soon. The problem would be that we are still restricted by human biology, you could make somebody super fast or super strong but that would still be within the limitations of biology. I think the way to make super soldiers, for now at least, is to use technology like robotics and computers.
The one aspect that I could see stem cells being very applicable for it wound healing, if you could treat a soldier with stem cells, or use regenerative medicine, you could speed up wound healing, meaning the soldier spends less time recovering.