Put your speculation hats on and come up with the craziest ideas you can, because there’s not much to go on for this one. Rockstar are working on the “next version of a famous IP” now that GTA V has shipped, according to one of their employee’s CVs.

What the game could be is anyone’s guess, although Take-Two have hinted at turning Red Dead into a “permanent franchise”, and with the success of that game a sequel seems like a logical step.
Rockstar New England – the developer in question – didn’t help develop RDR, though they did work on Bully: Scholarship Edition, Max Payne 3 and Grand Theft Auto V, though it’s probably too early for a new GTA or Max Payne title.
bigchrissyc
I hope its another RDR, on next gen. Which would make it even better.
TSBonyman
Grand Tabletennis Auto!
Eldave0
Really hope its Red Dead. Much prefer it to GTA
Kitch
Its got to be RDR I keep going back. Such a good looking game.