I specifically did say you won't catch all future requirements this way. But you want a mechanism to catch the reasonable and likely ones.
And for the unreasonable ones you can always say: "The system we originally intended wasn't meant to do this technically. If you want to have this feature we can help you but it will cost $X and this is a entirely new project."
If a graphic designer designs a logo and the customer in the end has the idea that they want that logo as a stamp or in a black and white version ANY graphic designer worth their salt will have anticipated this. If they want a 3D animated video of the whole thing rotating that is a different thing.
And for the unreasonable ones you can always say: "The system we originally intended wasn't meant to do this technically. If you want to have this feature we can help you but it will cost $X and this is a entirely new project."
If a graphic designer designs a logo and the customer in the end has the idea that they want that logo as a stamp or in a black and white version ANY graphic designer worth their salt will have anticipated this. If they want a 3D animated video of the whole thing rotating that is a different thing.