While it's a superb article, it strikes me as being distinctly aimed at laypeople, and I suspect someone who studied linguistics might already know large parts of it. (I haven't, but I know parts from having had Latin in school.)
(Also, it contains the words "This is not exactly what happened but it is basically what happened, please just fucking roll with it, this shit is long enough already." so I suspect there might be more in-depth material somewhere.)
Anyway, all of this is not aimed at you directly, but more of a general pondering of whether sending people articles on their subject matter is useful. Family members occasionally send me news articles on technology, which I usually find only moderately interesting.
This should be pretty common knowledge to any linguist who studied historical linguistics, although if you never did any historical linguistics you could easy miss that.
This should also be common knowledge to anyone who studied late-medieval Latin texts, as many of them use this feature to distinguish the 3 major Romance vernaculars of Europe, e.g. Dante's De Vulgari Eloquentia. There is even an entire region called Languedoc in France, which refers to the language its inhabitants speak (or used to speak).
Having say that, although I perfectly know about the distinction between languages of si, oil and oc, I was still intrigued enough to click on the article and it was a nice read (except for the tiny font) and I even learned something new: I didn't know that 'oc' was a calque from Gaulish 'to'.
The common case of people sending me articles about linguistics is worse: I often get heavily distorted pop-sci articles full of mistakes and misconceptions.
Actually, funnily enough Languedoc does not exist anymore, it has been merged with Midi-Pyrénées to form a new region called Occitanie.
There were quite a few debates about the name as former Occitan-speaking territories were much larger, and Perpignan and it's area are in the Occitanie region despite being Catalan.
Do you have any books to recommend for people who aren't interested in learning in-depth about historical linguistics, but like reading about the sort of interesting trivia found in the Tumblr post?
The point of the article is to say that using "this" in English as an affirmation is not a new phenomenon at all, and really, not wrong either (would we say it's wrong to say "oui" or "sí" or whatever is used in various Romance languages? no, we would not). That's a fair message to lay people and experts both.
(Sorry... Fantastic article in any case. I send anything similar to a friend who studied linguistics. This one is going to her immediately.)