Wiki tells me this idea was first used to describe social orders in the middle ages. Who were the key people writing about it and do more modern historians still draw on it?

What do Historians think about so called Fourth Estates such as independent media and trade unions? Are they still linked to the way Historians previously wrote about the Estates of the Realm, or are they an example of other subject areas adopting historical terminology?

Finally there’s the “Fifth Estate” (wiki leaks, blogs, twitter, even reddit) which is mainly an idea in sociology of media as far as I can tell. Are there links between this usage and what Historians have written on the other Estates?