With the new design and the fixed width, pages using PAGEBANNER get the banner limited to the width of the content, and not all the page. Once sticky header is deployed, this will get even more weird. Main projects using PAGEBANNER are Wikivoyage ones, but de.wikivoyage is not using it, and is the only Wikivoyage selected for the test phase, so we can't see this in action. Basque Wikipedia is using PAGEBANNER in all help pages (https://eu.wikipedia.org/wiki/Laguntza:Sarrera) and all Txikipedia pages (https://eu.wikipedia.org/wiki/Txikipedia:Sumendi).

PAGEBANNER can be a good feature, as it is the main picture showing up in the mobile app, but, as far as has been designed, there's no solution for it.