Upvote:2
Good question. I don't claim to know the full answer, but this quote from Mary Beard's SPQR might shed some light.
IN 212 CE the emperor Caracalla decreed that all the free inhabitants of the Roman Empire, wherever they lived, from Scotland to Syria, were Roman citizens. It was a revolutionary decision, which removed at a stroke the legal difference between the rulers and the ruled, and the culmination of a process that had been going on for almost a millennium. More than 30 million provincials became legally Roman overnight.
...
Citizenship, once granted to all, became irrelevant. Over the third century CE, it was the distinction between the honestiores (literally ‘the more honourable’, the rich elite, including veteran soldiers) and the humiliores (literally ‘the lower sort’) that came to matter and to divide Romans again into two groups, with unequal rights formally written into Roman law. It was, for example, only honestiores who were exempted, as all citizens once had been, from particularly cruel or degrading punishments, such as crucifixion or flogging. The ‘lower sort’ of citizens found themselves liable to the kind of penalties that had previously been reserved for slaves and non-citizens. The new boundary between insiders and outsiders followed the line of wealth, class and status.
It sounds like the patrician class persisted by another name. This is about 200 years after Augustus though, so there's a big gap to filled in by another repondent.