What should have happened in Wano: Zoro learning about his heritage, and visiting Ryuma's grave where he has a dream or vision of Oden and his life and fights, as well as him learning more about how great swords and forged and how black blades are made.
Tashigi would have gone to Wano as well, alongside Smoker, where they'd meet and work with X-Drake and learn about the Celestial Dragons and CP0's dirty deals with Kaido and Orochi, and with Tashigi learning about Wano culture, more lore on great swords and how they and black blades are made as well and learning techniques such as fire cutting, ice and lightning blade and others.
Zoro and Tashigi would also have some talk, with Zoro telling Tashigi about his backstory and Kuina.