What I believe is that he will raise Enma and Wado to supreme after he forges them black, Sandai will be great, I also believe he will acquire Shodai and make that black too, unless Nusjuro makes it black within their inevitable duel. Then I can see Zoro returning a mastered Sandai Kitetsu to the shop owner in Logue Town, in the end he will be an owner of two supreme sibling blades both created by Kozaburo and one blade that will be considered beyond Supreme.