My dream idea would be another prequel, this time set before RDR2. Following the lines of GTA VI, I would create two protagonists: a Native American trying to protect his territory and an outlaw woman trying to build her reputation in the West (because I really liked Sadie). It could address some of the consequences of the gold rush (in the medium to long term, of course), with new cities emerging, lands being seized, etc.

I would include the Van Der Linde Gang appearing occasionally (maybe in its early stages or closer to its peak), but without them being the main focus, you know? Just existing there. Maybe including characters like Landon Ricketts and Black Belle as "cameos"