The ability to fine-tune OOUI icon colors from the front end would be useful. An icon font would be an easy way to do this. Please consider including an OOUI webfont—and, ideally, a corresponding CSS file—with MediaWiki so skins and extensions could more easily use these icons. (A la this font by @Prtksxna, but bundled with MediaWiki.)

To provide a specific use case, the Refreshed skin features icons throughout its menus and buttons. The skin is designed to be customized, and various sites have changed the skin's colors via MediaWiki:Refreshed.css. Some devs have expressed interest in switching the skin to OOUI icons. However, Refreshed can't make the switch yet, since the icons are only available in a limited range of colors and they can't be customized through site CSS.

Edit: Just ran across T154957. Guess the font linked above actually came about in a previous discussion about Refreshed and MediaWiki... oops. :) I'm still a bit hesitant to settle exclusively for inline SVGs because dropping a bunch of those into a skin's PHP file doesn't seem very elegant.... But then again, seeing as any skins/extensions would probably only use a dozen icons at a time, loading a font with hundreds of icons doesn't seem great either. Curious to hear others' thoughts on how useful a font would be.