I don't see it plausible just because I feel there are better explanations, this one is very simple, it's hard to believe that Rome would impose an unchanging language to its people, and it sounds speculative, at least to me.
With the splitting of the Roman Empire into the Western Roman Empire and the Eastern Roman Empire, the Eastern Roman Empire ceased speaking Latin just because the now called Byzantine empire was mainly Greek, influenced by Greek culture and speaking the Greek language (the only exception being Romania, which was not in the Byzantine Empire as Rome had retreated from Dacia in 271 AD, thus it continued speaking a latin language).
Now, the Eastern Roman Empire existed for about 1000 years more than the Western One, falling in 1453 under the attack of the Turks. In this time, the Western Roman Empire had fallen, long ago (it's hard to define the year, many people consider the fall of the Western Roman Empire in 471, the year of the sacking of Rome by the Vandals).
So for a period of time, there was absolutely no authority in the area. Soon, because of the love of the Ostrogoths for Roman culture (known fact), when the first principalities emerged in that area, Roman culture was not lost. But there was absolutely no authority for some time. That's the moment when the 4 western Romance languages split. So what happened is exactly the opposite, because of the fall of the Roman Empire, when there was nobody to impose Latin, its accents became dialects, and then dialects became separate languages.
It's anyway known that Italian is mutually intelligible with Spanish, Spanish with Portuguese, Spanish with Catalan, most French can understand Italian, any Romanian understands Italian and Latin, and any Sardinian understands Italian and Latin.
That's my explanation, and I think it's much more plausible as it's actually backed up by historical facts, while that article seemed mostly a speculation.
