In an apparent interview with a Dutch gaming journalist from a gaming website, inside gamer. They apparently had a Q&A session with someone from Rockstar Games, and Rockstar answered a massive question. "Will the map from the original Red Dead Redemption be in Red Dead Redemption 2?" and supposedly, Rockstar answered "yes".
Below you can see the entire map from the original Red Dead Redemption. So, if this is true, this really could the biggest world, in size, that Rockstar has ever created.
Below is the translation from source. I have contacted Rockstar Games and are awaiting confirmation.
"This week a Dutch gaming journalist of insidegamer.nl/ got the chance to play Red Dead Redemption 2 for an entire day, and posted a Q&A article about it, in Dutch: http://www.insidegamer.nl/artikel/q-n-a-special-jouw-vragen-beantwoord-na-een-dag-red-redemption-2/. One of the questions asked (by me ;)) was the one burning on everyone's mind: is (part of) the map of Red Dead Redemption included in Red Dead Redemption 2?"
"The answer from a Rockstar rep: yes, it is."
Q: Are Armadillo and New Austin in the game?
A: Yup! After asking Rockstar they told me the entire (!) map of Red Dead Redemption is also in this game, but that of course there are many more areas added. In the six hours I played I only got to see a small part of Blackwater, and even that was already gigantic. Six hours was not enough to see any of the other familiar places.