I would love expanded multiplayer... maybe even true co-op.
 
I wouldn't want ti to become an MMO or anything persistent.... but Old West Boarderlands could be fun.

full coop campaign

Just another single-player story on par with Redemption's. All I need.

I don't know...RDR didn't really blow me away.  I don't think there was really anything wrong with it, it just wasn't my thing.  I like this idea of co-op though. 

More Red Harlow.

Fuck the multiplayer, I want a deeper single player experience. When I'm done, I want to say I cut some beef.

The ability to track and sneak attack (and possibly to set traps)cougars. This time is personal.

More emphasis on surviving in the wild. Not quite Snake Eater but with just abit more incentive to skin animals and collect herbs.

Stat improving elements, like the ones featured in San Andreas.

They also need the ability to be a gold prospector. 

" Stat improving elements, like the ones featured in San Andreas. "

I'd love a whole new story with a different character.

Radio on my horse. 

Cyber-punk cowboys riding cybernetic horses.

I wish they put more focus on the character development. As in not having the only conversations be getting mission objectives and the horse rides which got tedious fast.
 
I would've like to have heard more of Marston's thoughts, that was really my only problem with RDD.

A better Multiplayer system.

One giant steam powered mechanical spider.

I would have liked a more immersive free roam than the one from Redemption. I would like to earn cash, and I would hope they would provide more incentives to take part in other quests. Kinda like an MMORPG without the RPG parts. And taking part in various professions will be most welcome in my book.

radios in the horses.

Definitely a stronger single player.  They did a great job creating an immersive world, but forgot to put anything to do in it.
There seemed to be too much focus on the multiplayer which was honestly, dreadful.
 
Make the good parts better and focus less on the multiplayer stuff for mainstream appeal.  The game easily could have been GoTY.

Remove elements like...Mexico. Oh! And more moments like the entering Mexico/going to your house parts!

Guys... 
 
Picture a barren wasteland...with a thousand batmans at the horizon.
 
Introducing : Batman Freeroam

more red less dead

In my opinion they're 2 for 2, so I'm cool with just letting them do what they do.

" Definitely a stronger single player.  They did a great job creating an immersive world, but forgot to put anything to do in it. "

I want to see it be named Red Dead Revolution. 

A modern Red Dead Redemption that takes place in a sprawling urban jungle where crime, corruption, and the American dream expose themselves.
Er wait...

To be a Cowboy, not a Florist.

Since the game's best feature is its story, I would want more of the same. Full details in spoiler tags just in case: 
 

Better multiplayer.