On the command line it takes extra steps to discover the switches and arguments that a given command presents. It's easy to miss a specific incantation that will bring forth the full power of a given command in a given situation. Git, for example, has an amazingly rich command. It's hard to discover what you can do so most people end up using just the few commands that they absolutely need.
Just as TermKit offers a selectable list of directories when one types a path, it would be great if it could provide a structured way to build commands invocations, that presents options and perhaps help content as you go.
In addition to helping newbies dive in and get stuff done, it would help more experienced users continually advance their knowledge of how to get the most out of the tools they use.