Look at Chapter 972, and 973. Look at the narration box when Toki is reading the letter. Look at the narration box for the prophecy. Heck, look at the interrupted letter and continue reading it from where Toki starts her "prophecy". See that everything she is saying is in quotes. Now, look at the "prophecy",a nd see her reply. Isn't it obvious what she's replying to?"
The "look ahead to 20 years in the future" seems random, but the you read the full letter in the next chapter and it is clear what she was replying to.
It is *not* a prophecy. Toki was making a promise to the people of Wano that everything would be alright. All she had was hope.