If they traded for Darnold they would have three first rounders from that draft on the roster, Edmunds, Fitzpatrick and Darnold. They would need to decide on the fifth year options for 2022, Darnolds could be up to $25m by all accounts. I’d agree with @Formerscribe that it’d only be a viable option if Ben retires. I would not give up much for Darnold, late second at best, maybe even a third would do it. He is by no means a sure thing and even if he turns out to be a viable starter he will get expensive very quickly for any team that trades for him.