Rockstar Games have announced that Red Dead Online will be coming in November 2018 as a beta version, but the full release has no definite date yet. So far it seems to be a wild west themed version of the wildly successful GTA Online.
Games as a service are the most prolific cash cow trend and it would be unrealistic to expect Rockstar Games would pass up an opportunity to have it included in one of the most anticipated releases of 2018.
According to the official website, Red Dead Online will offer a new multiplayer experience for Red Dead Redemption 2 that wasn't available in the original Red Dead Redemption, since it will "evolve" the original formula by "blending narrative with competitive and cooperative gameplay in fun new ways".
Technically, the original game also had competitive and cooperative gameplay but the evolution Rockstar mentioned will likely revolve around multiplayer in an open world, much like in GTA Online. This will leave potential adventures and fun times at the mercy of the players' creativity, which is usually the thing that yields the best results. Bethesda have been pulling it off for years by leaving room for modders to fix their games.
Considering the initial beta launch is scheduled for November 2018, it is safe to say Rockstar will first focus on fixing and stabilising the initial singleplayer release so those who are not multiplayer enthusiasts don't have a reason to worry yet.
Rockstar seem to be aware that the scale of Red Dead Redemption 2 will present a challenge in itself, especially when the online component comes into place. They announced that the company is "looking forward to working with [Red Dead Redemption 2's] amazing and dedicated community to share ideas, help [Rockstar] fix teething problems" and fix major problems that might occur with the launch.
There is no direct mention of microtransactions, but the potential GTA Online showed as a cash cow doesn't leave much room for debate. Let's just hope they don't eventually introduce mechanical arm cosmetics and call them historically accurate. Unless Rockstar does in the company's that is.