It's not the only major game to have released in 2018, and the only tangible "source" for RDR2 on switch was the image of a switch pro controller appearing in the game files. That's very thin, and can have numerous other interpretations.
From the point of view of business, GTA 5 makes way more sense, and it never materialized for reasons we ignored; what we can be sure of is that those issues will also exist for RDR2, and are probably even worse.
I don't think RDR2 isn't feasible, as I previously said in this thread. But it just doesn't make much sense.