The Horizontal Orientation Slicer adds nice functionality but other buttons like the Bookmark/Page navigator have richer customization such as shapes and styles for each state (Default, Hover, Press...
I was also about to post the same idea. Since introduction of field parameters, using slicer with "tiles" with field parameters has enabled designing reports with much more options for the end users compared to how clumsy and laborious bookmarks and different visuals or pages for the same this where but from a point of view of a developer with a focus on UI, this lack of formatting options is now a huge issue because good UI is consistent and at the moment Power BI options make this pretty impossible.
