If you select a sub-object (Ctrl+Shift+Click) before running the SoftTransform command, the SoftTransform will display a sphere of influence. The sphere of influence is shown in the following screenshot. You can change its radius with a mouse, or by typing a number in the command prompt.
I hope that the sphere of influence will evolve into clickable widget (like gumball), and that its shape will provide a clue about current shape option.
Yes. This is real problem, but it has elegant solution. Instead of adding clutter to the Rhino interface (e.g. status bar), the sphere of influence (show above) can be the clue that the SoftTransform command has been enabled. The SoftTransform command has no effect on Rhino objects - its sole purpose is editing/changing Rhino sub-objects. If the SoftTransform command has been enabled when you select the sub-object, the sphere of influence should be automatically displayed to give you the clue that the SoftTransform command has been enabled. If the SoftTransform command has not been enabled, the sphere of influence should not be displayed.
The SoftTransform command has four kinds of falloff: smooth, linear, round, and sharp. The falloff is changed with shape option. I have no clue how these falloffs work because the SoftTransform command still does not have any documentation.
By the way, bad documentation is not just Rhino problem - nobody cares about documentation. 
During the Second World War German army was the best army in the world because it was the only army that had good documentation. For example, German tank manuals were illustrated with good drawings. Other countries had horrible tank manuals.