Like they said. Without the Renaissance with its rebirth in interest in Latin, and thus the etymological roots of French, those endings would have probably fallen away in the 16th century, before colonisation. Hell, Latinists even decided to "correct" the language by retrograding spelling, deliberately adding back in letters and recreating words to show a greater link to Latin. An example I can give without a lot of explaining is the Latin word "frágilis." Natural evolution over the centuries gave us the word "frêle" (from which the English "frail"). That wasn't Latin enough though, so they added the word "fragile" to French, even though it meant the exact same thing.
So yeah, it'd be more plausible to create a TL where the neologues in France are allowed to run amok to the point where there's a movement to repronounce endings and plurals than to see that happen in America.