Honestly, I am fine trading Vaughn if the return is mid to top rotation pre-arb or arb1 SP. Not exactly sure who would fit that description that could be available tho. Trading Madrigal makes zero sense.
And FG projects Nova at 1.3 fWAR for 2020. WAR is a counting stat - and they project Gio to throw 150 IP. Nova pitched nearly 200 last year. FG has Nova at 165 IP on the 1.3 fWAR projection. So, in other words, they prefer Gio.
Having too many SP is a good problem to have and certainly one the Sox will be happy to address if need be. Guys get hurt. Guys are ineffective. Shit happens.
But I do think you pretty much hit the nail on the head on why the Sox aren't super keen on backing up the truck for a long term deal for sketchy long term assets like Ryu and Keuchel.
They're never going to officially say this until they option him to the minors in March. So no. But the people in charge have alluded to it many times. So yah, Kopech is going to be in AAA. Stop penciling him into your OD rotations.