I guess what happened with GTA Trilogy: Definitive Edition scared Rockstar so much they decided "fuck it, just do a 1:1 port, we're not touching a damn thing." Notice Xbox isn't included in this announcement, and I think I know why. On Xbox you can just play the 2010 release of RDR1 via backwards compatibility, so Rockstar probably figured it ain't worth doing a "native" port. The studio handling the port is NOT Grove Street Games, the one that handled the infamous GTA Trilogy collection, but rather Double Eleven, a studio founded by former Rockstar devs who are mainly known for providing development assistance and ports (such as porting Little Big Planet to the Vita and bringing Rust to consoles).
Honestly dunno how I feel about this announcement because hey I imagine for people who only game on PlayStation or Nintendo this is awesome news, but for people who were hoping maybe it'd be a remaster with Red Dead Redemption 2's visuals will be disappointed. I'm personally most curious about the Switch version, it's a handheld that can handle ports of games from the Xbox 360 era no problem, but I believe there have still been occasions where what should have been an easy port still missed the mark by a wide margin.