User blog comment:Brandon Rhea/Wiki Modernization Stage Two: Page and Article Headers/@comment-8479011-20170316194525/@comment-20644-20170316201553

Customization will be allowed via Theme Designer in terms of what you can use as your wordmark, what color the header is, and what the background/header image is. Whether we allow additional CSS-based customizations is what we're currently figuring out. But for now we want to see how this test performs before we make any final decisions on the customization front. That's still a few weeks out.