> My initial impression is that the ROI does not justify the effort.
> It depends on how strongly users respond to the feature, because it'll create a noticeable amount of work for writers.
The author is probably correct about the ROI not justifying the effort, but I think UI design should also be considered as an input for whether users would respond to the feature. The UI as it stands is technically functional and easy to understand, but not exactly effortless or convenient to use. In particular, there's quite a jarring difference between the modes during switch, making comparison impossible.
An inline UI next to/within the content, with some logic to ensure the nearest content to the control stays at the same scroll-position during change would help a lot with this.
e.g. Expounder (linked in a sibling comment) looks to be a much nicer UI implementation from my quick glance at it.