That where legibility matters, a sans font is the wrong place to start, or stop.
Sans faces appeal to graphic designers for graphic-design reasons that have no connection to merit as a means to convey useful information clearly and quickly. Graphic designers prefer details that make text less legible for the actual people obliged to read it, who get no say in what is used.
I have experimented with this for a long time, and I find that serifs make more sense for books, and generally large volumes of uninterrupted text, while sans-serifs make more sense for labels and other chrome.
Interestingly, on the web, I still prefer sans-serif (Verdana especially). But perhaps it's because more than a page of two of text is relatively rare, and most sites are really more like apps in layout - a menu, various labels and buttons etc. Or interactive discussion like here, where each comment stands by itself.
For book readers, Amazon's Bookerly is just perfect for reading hours straight. It's not as condensed as many serif fonts, and it keeps all strokes full-bodies, which makes it a lot easier on the eyes, IMO.
Not really. A handful of letters have serif-like features, but that's true of a lot of typefaces normally classified as "sans serif".
The reality, of course, is that there's a vast grey area between "serif typeface" and "sans serif typeface", and this one does sit in that grey area, albeit much closer to the "sans serif" side.
When will they learn? When will we?