A most interesting and honorable idea you have brought forward.
Alas i suspect Rockstar is in several aspects not, in my own view, the most suitable developer for a potential title that were to explore a narrative storyline from a Native American outset.
Rockstar games narrative manners are within a twilight region in-between a classic and revisionist style, at least as of the latest output of theirs.
Earlier, during the redevelopmental stages of the series (Red Dead) first title, a former Capcom game that was later purcased and then finally released as Red Dead Revolver by Rockstar Games, a heavily spaghetti western inspired style, and a more classical western storyline was applied to a game that as of predominantly comical and (in some aspects) fantasy based.
Even if done correctly, the majority of source material (Revolver included) proves that Native American characters are represented in a unfavourable manner, in some cases of italian productions from the 1960s and 1970s, even the chosen actors of characters portrayed as Native American are bizarre as well as questionable (Navajo Joe stars Burt Reynolds as a Native American protagonist, that sets the mental picture of the absurdity born out of minds that had no comprehension of required concept).
Red Dead Redemption did a complete rehaul of the overall stylistic narrative representation, although with a heavy emhasis on a cynical, fatalistic view of a long dead era.
Characters are often, if not mostly, portayed as from a cold, defeatist view, and also seem to end up dead or at one or other form of loss in the end.
Redemption had a rather uncomfortable presentation of any Native American character, and as one tries to recall any of said characters, only one springs to mind as a none antagonistic and none hostile character.
This character is killed point blank by another Native American, one of every other unfortunatelly questionable portrayal of the kind.
Redemption 2 continues to display a very classical view of the subject, and not in a all ways preferrable manner.
Having to explain the realities of history to children playing the game (yes children subjected to the title) because of their misconseptions as to a narration set out of view from a character not of Native American decent, is alarming.
Rockstar games are not a source of historical re-enactment, not a source of simulation based reality projects, not a creator of factual media, not meant for children or teens as a interactive medium, and still they recieve a heavy amount of critical backlash for the afformentioned aspects, in eighter lack or claimed accelerative psychological deteriation of a societally implemented structure, of userbases that should not be able to be in interaction of their products.
Cultural, litterary, historical, narration aspect based, writer style and many more reasons are behind the reason i find Rockstar to be a unsuitable choise to contact.
The basic storyline of the next Red Dead title is probably within the minds of the script editors/writers of Redemtion 2, thus i find it doubtful that any title of the series that would be outside of the whole storyline of the current cast would even be developed before the end of the decade.
The Red Dead series are stylistically a breed of it's own, and lone gunmen like Morgan and Marston are likely the upcoming protagonists as well.
A more suitable candidate of a video game title that i believe would be capable of creating a realistic as well as functioning output would be Activision, that has shown their capabilites during the PS2 era with the critically acclaimed title GUN.
The series has never recieved a sequel, fans of the game have waited for a second title ever since the former title was released, the protagonist of GUN and his heritage if Native American, and the storyline was well written.
GUN itself recieved controversy concerning portayal of minority stereotypes, allthough, compared to the current atmosphere of conciense, i find that a upcoming title would be with the right source material a better representative of values.
The whole era of old west is well known for instances of completely horrid and moral distastefulness, not only among different race aspects or full scale military conflict causal to these tragical events, but also general actions of societal views today classed as horrible.
Also, as Rockstar releases a title from 2013 as a "updated", "new" game for the PS5 era as one of their new titles, have barely released any new titles for the last generation as well, comparing Activision to them is also preferrable..
Activision are bordering comically efficient in title releases, and have rather a more realistic output to create a new series, where Rockstar could collapse if one main title failed for them.
I do wish to point out that this comment is merely a personal view of the subject matter, based on own concept and views, thus potentially neglecting to take potential positives in account, and i do truly hope your idea would create a seed that grows into a flourishing tree.
F. Whitelaw.Keema