Keyboard-only is decent for text, and particularly good for text where everything that needs to be edited will be on the screen at the same time.
Because I kept the mouse in right-hand configuration, I can use any mouse with my left hand without having to switch the buttons, and I can also still use the mouse right-handed.
I call this model the "MOBA interaction model", because in those games (which include League, Smite, and Dota) you must place do exactly this.
I, too, wish that more interfaces worked this way - but there's a fundamental problem, which is that many tools (including all Unix ones) are more efficient when you can input text, which necessitates the use of both hands on the keyboard.
Which would suck for left handed people.
As for the right, as some other commenters have noted it really isn't that bad to use your non-dominant hand with a mouse. Most of the movement precision comes from the wrist and elbow, rather than finer finger control.