This site apparently got info last summer regarding these rumors, but didn't publish because they couldn't verify anything.
The rumors included unseen images of Arthur Morgan and Dutch van der Linde, which match the shots of the characters in the second Red Dead Redemption 2 trailer, so they are treating them as legit leaks for now (but still unconfirmed).
Among the leaks (much more info in the article):
Multiplayer modes: Battle Royale, Revive and Survive, Money Grab
GTA online style apartments return in the form of camping tents
Companion app to launch alongside the game
Main campaign and multiplayer fully playable in 1st person (though come on, you've gotta play this in 3rd person to see your character!)
Eagle Eye is returning - edit: article calls it Eagle Eye, but is probably Dead Eye
Fishing as a side activity
http://www.trustedreviews.com/news/red-dead-redemption-2-leak-reveals-battle-royale-first-person-more-3388634