Season Exclusive cards are a bit of an RNG chore at the moment if I'm perfectly honest. You spend an entire season grinding points for boxes to be left after 3 months with maybe 1 or 2 regularly usable cards. I suspect most players (like me) have bronze and above ''best'' or ''Favorite'' cards for the mercs they play regularly so the only time one of the ''Exclusive'' cards will be of any use is if they match the favored card.
So when the season is up you are left with an inventory filled with cards you will never use and can't trade in.
My suggestion would be either let people trade in the Season cards for an amount of loadout fragments equal or greater than the equivalent of a cobalt
or Add in a system to ''Re-roll'' a card for either 20k credits, 5k loadout fragments or microtrans.
I think this would be doubly useful as it could act as a credit-sink for those of us who have purchased all the mercs and have nothing to spend credits on. Would give people a reason to farm credits again and also lessen the blow of opening boxes to find nothing usable.