Sure, the One Piece manga is still in the Wano Arc. There are many intense battles and plot twists happening. The arc has been quite elaborate and full of surprises.
One interesting 'One Piece Wano fanfiction' could be about a new character who is a master swordsman from Wano and teams up with Zoro. They go on adventures within Wano, facing off against new and powerful enemies that were not shown in the original story. This could add more depth to the already rich Wano arc.
First, you need to have a good understanding of the One Piece world, especially the Wano arc. Read the manga or watch the anime carefully. Then, think of an interesting concept. It could be a new adventure for the characters, a different outcome for an existing event, or a story centered around a minor character. After that, start creating your characters (if any new ones) and plan out the plot.
RWBY's understanding could change in several ways. They could see how fans interpret the power systems in One Piece in unique ways in the fanfiction. Also, they might get a better sense of the world - building, like how different islands are portrayed. They could also start to think about how One Piece's themes of friendship and adventure can be applied in different scenarios presented in the fanfiction.
After episode 1000, it's best to start with the chapter that directly continues the story. You can find this by checking the official manga release or referring to manga reading platforms that provide the correct sequence.
I'd suggest starting from the chapter that corresponds to episode 1060. You can check online manga forums or dedicated manga sites for the exact chapter number.