User blog comment:Brandon Rhea/New Page and Article Headers: Official Release Date/@comment-5952365-20170811072457/@comment-26923519-20170811090235

Me too. However, the only disadvantage to it, IMO, is the fact that we are heavily limited from customization. Sure, they can limit some customizations that take it too far like ExtendedNavigation, and I understand why that was disallowed, but the FANDOM staff should've let us use at least some CSS Site-Wide, like MovingWordmark, main page title removal, UTC Clock and a handful of other scripts and customzations.

I know they want to provide consistency, but IMO, the community header is a part of a wiki, not the entire site. It's like being forced to provide material design in Google apps. This is just a random example, BTW, but you get the point. So IMO, if they want to provide consistency, they can heavily limit JS page header customization to the point where you can only add more Edit menu items and icons about articles, and slightly limit CSS page header customization.