NO! I think you are going TOO far with tidying the ship. Appreciate efforts overall, but there is no need to absolutely standardize the banner. I think it is enough to ask bakers to always use the Iwo Jima image centrally and respectfully. Bakers who deviate too much and make banners that are disrespectful do and will get called out. As long as the Iwo Jima image is used as stated, anons can easily find the current thread and there is continuity, both of which were the primary concerns expressed.

I really like the creativity of the banners and the energy they bring to the breads. The only times new banners are a problem for finding the thread is if they don't have the Iwo Jima image big enough or centrally located for easy visual recognition. And I don't think using anything silly is appropriate. Those would be the two pieces of guidance I would suggest.

Perhaps it could be stated that anons should flag/report any banner that is a problem, and you could edit the post to swap out that banner with a generic one if it has more than three reports on it.