I have an idea for Red Dead Redemption 3 it involves Mary (Arthur's ex)
On the first Mary mission where she sends you a letter to meet her on a farm she tells Arthur that the dude she married over Arthur died of pneumonia.
I thought
What if, in RDR3 we play as this unknown guy who stole Mary from Arthur (make Arthur somewhat of a rival to this guy, both vying for her love) he's also an outlaw, miscreant like Arthur but Mary has no clue, is also from a different gang and leads a double life. He's dies of pneumonia at the end. It'd be
because we'd still be dealing with Mary Linton again but we'd get to see young Arthur frequently and cameos of Dutch and Hosea.
They can really go any direction with the red dead franchise since they have so many vague references to off screen characters that could be fleshed out.