They said it's all from scratch and takes time (logically so), and I these threads prove how often they would have to change it Lol. Someone makes a thread saying, "oh so and so should be here now", and then another week something else big may happen.
You can try to argue that there haven't been a significant sequence of changes, but then how would they have known that? You can only know that when you compare "then" to the "now", but you first have to arrive to the "now". So it would be extremely exhaustive to change it every time something happens in the manga that would justifty a change.
Also, they say it's not meant to represent the changes in the manga. The next banner can even have just two people on it lol (maybe Sasuke and Naruto). The design is up to them and the artist.
Having said that, of course I wouldn't mind seeing something new up there. Though, that's the at the back of my mind whenever I browse NB.
I'm neutral on this suggestion, but if they accept it, great!