According to the leaker who made a post on 4Chan the game will be a full blown remake of RDR1 in Red Dead Redemption 2‘s engine. The game will also have enhancements from RDR2 like hunting and fishing.
The Remake is currently being developed by Rockstar India, Rockstar San Diego and Ruffian Games. Ruffian Games previously worked on the development of the Master Chief Collection, so they have some experience bringing old games back with new technology.
The leaker behind this is Chris Liberty, who’s a relatively new leaker that claims to be up to date with GTA VI’s development. (Tap on the images for full resolution)
The Red Dead Redemption Remake according to the leak is currently approaching late stages of development and is expected to release in Q1 or Q2 of 2021. The leak also stated that GTA VI is still sometime away, with the expected announcement to be somewhere around Summer 2022.
One more thing, the game probably won’t have RDR Online but will include the Undead Nightmare DLC.
As always take leaks with your favorite cooking seasoning till we get an official evidence to back it up.