I know but as you remember Wano was something he wanted to write since the beginning of the story and as of now it looks like ehh.
Eh, he never said that. Just that he wanted to go there for a long time, at least since introducing Ryuuma. We know at least portions of the plotline existed then since Moria/Kaido's feud was mentioned then too.
I wouldn't say it was this big plotline he conceived in the late 1990's, only that he really wanted to draw Japanese culture as an island and he had some crazy ideas for it (which he has for Wano, and thats cool)
EoS/Shanks are things hes had since the beginning, that is what we know of.