The thing about GTAO is that it's central pastiche is that everything is driven by greed. The game, both SP and MP, is essentially about trying to get as rich as possible and buy up everything in sight. There is nothing at all inherent in that in the Western either as fiction or history, though, so it has no place at all in RDO. While it's certainly possible to make a go out of being a Rockefeller, Vanderbilt or Carnegie robber baron expanding your empire across the West, that's really not what people look for in a Western novel, movie, TV show, and certainly not in a video game.
I think RDR1 had a great multiplayer experience for minigames, but the free roam had very little to do beyond turn into a PVP killbox for all the other players who were bored out of their skulls. So what I'd like to see for RDO is very real results for you as a single player, and/or as a posse/gang. The Wild West is about making a name for yourself, not about getting rich. So everything should be about establishing a reputation, good or evil, and always trying to be the fastest gun in the West. Or the best hunter, or best gambler, or best rodeo rider, whatever you want to focus on. Instead of earning $$$, it should be about earning rep, and you can use that rep to "buy" stylish gear, unique horses, customize your home or your steed or yourself. Earn titles and literal badges. Run for office --- from sheriff of a one-horse town all the way up to Governor of a new Territory. Maybe even President. Have newspaper reporters seek you out for their headlines, or even dime store novelists write a biography about you. Maybe attract key NPCs to your side. Hell, even something as simple as raise a family.
GTAO is about getting rich. RDO should be about getting famous. A true Legend of the West. IMHO, that's where the difference between GTAO and RDO should begin, and end.