You know, as cool as it would be for Zoro’s swords to eat the Seiryu fruit, it would actually be redundant.
What does the dragon fruit provide?
-increased durability
-fire breath
-wind scythes
-tornado
-cutting tornado
-flight
Zoro’s swords can already produce fire, he has air slashes, tatsumaki, and they are extremely durable already. I guess his swords can fly him. But for the most part, Oda was operating on rule of cool rather than practicality when he said he’d rather Zoro’s swords eat the fruit instead of himself.