There could be trade up scenarios among other teams for other players as well, e.g. Barkley, Chubb, Fitzpatrick, Nelson etc. Not that any of them are necessarily worthy of the #2, but when you have other teams jamming up the top 5-6 of the draft, it might incent teams to do what they must to get the player they want (at least in theory). Also, I wouldn't rule out the Bills putting together a massive package including their 12, 21, 2nd rounder and future picks. Also, many of the trade scenarios and team interest likely depends on who the browns draft and don't draft with their #1 overall pick. For instance, I think the interest from teams changes if the Browns pass on Barkely.
I still say we shouldn't pass on Darnold if he's there. If not, I recommend trading down, and I am increasingly luke warm on Mayfield, Rosen, and especially Josh Allen.