Olga Vasileva, writing at Diff (a blog ran by the WIkimedia volunteer community) about the new look that’s coming to Wikipedia, and also why they’re making the changes now:
Wikipedia has remained a critical and widely-used resource for knowledge across the world for the past two decades. Over this time, the site has expanded significantly to contain unparalleled amounts of reliable and thorough information, including 53 million articles across over 300 languages. While Wikipedia’s content has grown rapidly, our interface has not kept pace. We’re proud that our website is more direct, simple, and advertisement-free than the rest of the internet. Yet, the design of desktop Wikipedia and other Wikimedia Foundation projects have not seen any substantive changes for the past 10 years, leaving certain elements of the site’s navigation feeling clunky and overwhelming to readers and editors whose main purpose is to create, learn, and curate content.
There’s no definitive list yet on the differences that will be coming in the new design. But the improvements will include things like a max content width, collapsible sidebar, sticky headers, more prominent search bar and table of contents, and a few other things. You can see a few of these concepts on MediaWiki.