I played the event Inheritance, and selected the Action - Reserve card Duplicate. Afterwards, while I was able to play my estates as Duplicates, I was never prompted when I gained a card worth 6 or less, to see if I wanted to call up the Duplicate on my mat and gain a copy of that card
Unfortunately, this is correct behaviour after the September 2019 shapeshifter rules update. Inheritanc now reads:
Inheritance: Event, $7
Once per game: Set aside a non-Command Action card from the Supply costing up to $4. Move your Estate token to it. (During your turns, Estates are also Actions with "Play the card with your Estate token, leaving it there.")
Note the sentence in parenthesis: The Estates no longer "become" Duplicates, they just play the Duplicate that was set aside. And since the set aside Duplicate can't move to the Tavern Mat (it expected itself in play), it can never be called.
So to say that in no uncertain terms: Inheriting Duplicate under the new rules is (in 99.9% of cases) a really bad move, as your Estates simply "Do nothing" when played.