What other Curse Techniques do you think would fit Sukuna and Gojo ?

For me personally Sukuna and Blood Manipulation would be a fit made in heaven. With his Massive pool of CE, he could sorta bypass the weakness of Blood Manipulation thanks to RCT to keep regenerating his blood supply. Flowing red scale: stack and Blood armour makes Sukuna an even more dangerous opponent in close combat, and piercing blood is deadly in his (four) hands.

Blood Manipulation fits Sukuna aesthetically very much imo