ok so i had an idea recently about a remade version of rdr1, which includes Sadie and Charles.
i'll leave this plain and simple because if a remake does happen for rdr1, this is how i imagine it:
basically the same thing except Sadie and Charles are Assisting john. i know Charles went to Canada and Sadie went somewhere else in america... i forgot, but perhaps they got forced back by could get forced back by the government in some way? (maybe Charles starts a family in Canada and the american government cuts a deal with the Canadians to bring Charles back there to force him to assist them or else they'll execute his family and him or something. i can't imagine anything for Sadie being forced back except her not wanting john and/or Charles family getting hurt because she likely wouldn't start a new one with losing jack)
i'm not gonna act like i know what your thinking of but personally this is what i imagine rockstar doing, pulling the "you can play as all three of them" like they did for Gta5 seems likely if a remake for rdr1 is to happen. plus this works somewhat well for a backstory for what hey did before the events of rdr1 and after the events of rdr2 and maybe completes their story...
and everybody wants to play as Miss Adler anyways
also i think a rdr2 zombie game would be interesting just for the alternate timeline (basically those who died in rdr2 instead live and those who lived died.)