I got this to work on the TEXT on the button only.
It worked fine for me. Setting Fill color based on a formula changed the button color. The other changes are all text based so by default they are only going to change the text formatting.
Note that a button is a graphic object with text inside of it. The Conditional Formatting are mostly for text changes so that is the limitation.
I am not sure what you are saying, maybe I am missing something. But "buttons" have been able to be conditionally formatted since the option existed, FM9. Even without anything assigned to it a "Button" could always be conditionally formatted.