I really wish there were more historical RPGs similar in spirit to Kingdom Come: Deliverance, but in particular, one based around the American Revolution or Civil War.
For example, I have this idea in my head for a game with a very long (rectangular instead of square) map covering the Mississippi River. There would be three major cities of New Orleans, St. Louis, and Chicago, and it would run all the way from the Louisiana bayous to the Minnesota-Canada border. I don't know how far east or west it should go, exactly, but I like to imagine it maybe going about one state over on the eastern part (just the western thirds of Tennessee and Kentucky) and two states over on the western part.
In this space you have a little bit of everything terrain-wise. Bayou (Louisiana), hot humid forests (Mississippi), light woodland mountains (Ozarks), desert (South Texas), plains, flat woodlands (Illinois), thick snowy forests (Minnesota), badlands (Dakotas). The setting would be the American Civil War, maybe in a three-act structure running from the 1850s to 1870s, so you'd have the development from Bleeding Kansas to the Redeemers. It could be more of an open RPG like Fallout (w. guns) or a narrower game like Red Dead Redemption. "Muh muskets" is no excuse not to have such a game, because six-shooters existed over the whole period, along with various repeaters, breechloaders, etc., and muskets if anything add to the excitement by being one-shot weapons which you then use as clubs/spears or set aside to close in with melee weapons. You could make an interesting combat system out of literally any time period, and that includes the Revolutionary and Civil War eras.
For a smaller-scale game with a Civil War theme, you could have something like Kingdom Come: Deliverance w. guns but set in the Cumberland Plateau with freedom to choose faction, or the Indian Territory.
An open world game in Texas would also be really good, and not necessarily a historical one either. Texas would be perfect for a GTA: San Andreas like treatment, with its four major divisions (the Deep South-like east, the Great Plains-like north, the Southwest-like south and west, and the Hill Country) and its heritage and major cities. I don't understand why basically nobody has made a video game set in Texas in any time period.