I don't know. At school, Villon is the limit, anyone after him is fair game in exams, competitions etc. and before him it's considered to be specialised knowledge. The difference in language between him and medieval poets isn't that big, and they're all intelligible to modern eyes if said eyes are trained enough (we've had the Académie Française since Richelieu, meaning that written French doesn't evolve as quickly as other languages, only slang and dialects change with every other generation). I think arbitrarily choosing Villon is more of an ideological choice, as in making the beginnings of French coincide with the Renaissance.