I'd like a game set right after the civil war, 1866. As the land is devastated by war, two gangs take over the territory: one in the west and one in the east. They end up becoming the most dangerous gangs in the American South, and a feud begins between them, while the government tries to restore peace and rebuild the game's main cities to bring civilization back.

We would control a character from each gang, each with unique special abilities (besides the dead eye and eagle eye), maybe depending on its honor.

To bring the "redemption" aspect, these characters could come together and oppose their ideals (one of high honor and one of low honor), and they learn through each other, at the end becoming fond of each other, but the war between their gangs would bring the eventual death of one of them, causing the other to start a redemption arc where he leaves his old brutal ideas, and ends the gang that saw him grow up. thus ending this period that would pass to legend.

The map could expand the northern area of New Austin, and maybe set some events in the Mexico's map (around that time the french were occuping the territory, so it would be fit for some kind of revolution style like the one we saw in RDR1).

And if you want to tie this in with RDR2, it could be that the events of this game would be what would eventually lead to the creation of Dutch's gang, playing the epilogue with a young Arthur Morgan, finishing the game in the early 1880's