Assuming RDR3 is gonna finish the story of the Van Der Linde Gang. What kind of stories should the franchise explore in future games?
I personally think it should explore life as a Native fighting against the Government. Play as someone similar to Eagle Flies.
Another story that could be interesting is less of a story and more of a simulator. You play as a Lawman in any town or city and you start at any point in time. If it's a bigger city, you would not start in any high ranks, but if you are the only lawman in a town, you're the sheriff(Which would also put you in charge of stopping crime in the whole county). As time progresses, the town/city will grow, meaning more crime will occur. This will bring up the need to hire deputies. I'd say the game ends at around 1945. It would be very fun to play as this side of the law, just keeping the people of your town safe.
I think an interesting story would be of a Mexican revolutionary, who moves to the US to recruit members, then heads back into Mexico to take the government. I'd say this takes place in a different universe, like Revolver.
Quick ideas time: Lawman turned criminal, assassin, fictional second US civil war taking place in 1889, very early mafia (assumed to inspire the mafias of the 1920's in this universe)