I think that when you distill Jim’s work into practice, it is only applicable for high precision applications. I don’t think it can be used in most sports, street, or wildlife photography. I didn’t know that ETTR is only useful at base ISO. There are many conditions where such shooting is not possible.
But if you’re doing studio or landscape photography, it delivers the best results. In fact, I could see a studio photographer taking this a step farther, by shooting test images and opening them up in a RAW histogram viewer on a PC, and adjusting exposure as needed.
I'm still struggling with your discussion of the Hasselblad shot. You said there was no clipping in the original shot and you supported that proposition by posting the raw histogram for that version followed by a raw histogram for a +1/3 Ev version of the scene. Although the original version doesn't have as much clipping in the green channels as the +1/3 version (of course), the raw histogram DOES clearly indicate that there are max'd out green pixels. Thus, the in-camera histogram indication for the green channel really isn't misleading in any meaningful way, as far as I'm concerned. The inclusion of the post-conversion histograms from Lightroom and Phocus doesn't really add any clarification to the question of how much (if at all) the in-camera histogram is off. Slight differences in default raw converter behavior (including the amount of any highlight shouldering and reconstruction in Adobe's converter) are to be expected and tell us nothing helpful about the in-camera histogram particulars in play with your Hasselblad.
Moreover, the observation that the in-camera histogram continued to show green channel clipping until -1 2/3 Ev relative to the so-called ETTR version is just confirmation of the (near) specular nature of the very small number of clipped green pixels that are present in the white flowers. These (near) specular highlights are commonly encountered in shots that feature sunlit flowers. The missed lesson here that could have been explained to your readers is how troublesome such highlights can be when relying on in-camera histograms and blinkies for optimizing exposure. Specular highlights are the primary reason, of course, for qualifying your advice at the end of the article to "Check the histogram or the zebras to make sure you’re not going to clip any important highlights." The key word in your end-of-article advice is "important," and it's one that isn't really addressed at all. In my experience, the challenge of distinguishing "important" from non-important highlights when reading histograms/blinkies is usually a bigger challenge to effective exposure optimization than the other issues (the impact of application of WB co-efficients and tone curves) that are emphasized.
A successful ETTR photographer needs to be able to recognize why the green channel "clipping" shown in the in-camera histogram of your example isn't important either in the sense that clipping certain highlights are often acceptable relative to the lower tonal SNR benefits to be gained but ALSO in the sense that these green channel-only clipped highlights pose no problem for recovery in a competent raw converter. Without integrating a raw conversion and post-conversion strategy into one's thinking about the optimal exposure determination in the field (ala Adams' previsualization and zone system thinking), ETTRing quickly becomes counterproductive and discouraging (as we've now seen in this very thread).
When I was shooting film, especially slide film, I used the Weston meter with the Invercone and got good exposures. You could do the same on digital with fully manual settings.
However, I usually set digital cameras to evaluative metering, which I find works well.