The term "expose to the right" referring to the histogram is a new term for me as I'm not someone who has spent any time thinking about digital exposure techniques.
But my 1975 copy of "Photographic Sensitometry" by Zakia and Todd does. They spend a lot of time illustrating the concept - even though they don't call it ETTR. They have a scene showing a properly exposed negative printed to give the "best" print. They also show "best" prints made from negatives that are 2, 4, and 6 stops under & over exposed. Their premise supported by the prints is that a negative 6 stops overexposed is still capable of making an "excellent" (their descriptive terms, not mine), while a negative underexposed by two stops is incapable of an "excellent" print. While the prints in the book certainly support their thesis, I've always felt it was an odd photograph to use - but the scene was chosen in the thought process of scientists/engineers rather than artists.
The Zakia & Todd book is wonderful in explaining exposure and resulting negatives from an engineering point of view. It certainly is not weighed down by any subjective artistic mumbo jumbo.
SEI exposure meters were set up to provide exposure information on values placed on Zone II to insure that there always was enough exposure to get the low values.
So to sum up. My approach has always been that underexposure is death, and overexposure is the preferable MISTAKE. And I believe Picker's message was basically the same, but he wanted to make exposures that were the bare minimum for the scene.