I agree, soft shelled crabs don't need a lot of accoutrements. I dust mine well with flour seasoned with salt and pepper and fry in a 50-50 mix of butter and olive oil and serve plain and hot on soft potato rolls with a little tartar sauce. I'd gladly serve summer tomatoes on the side, since the flavors would meld nicely, but never ON the sandwich. As for pancetta, it strikes me as a wholly unnecessary affectation in this context.
Too too many ingredients as less is more. A salty old timer Marylander who first brought me just fished soft shell Crabsvshowed me how to clean them ,?have my first delicious taste of them, having NOTHING added , a must👌❤️🎼😍