I'd like the ability to set/override the default font for individual items in a ComboBox or ListBox (like we already can for table rows/columns).
For a recent use case, I was using a ListBox to show information in a tree, where I wanted to make a particular entry standout by using a bold font. At which point, I remembered you can't set item fonts (something I've wanted to do before over the years).
The same applies to ComboBox as you may also want to show a tree in a drop-down with items that standout with a different font.
Another scenario that comes to mind is providing users with the ability to select a font (i.e. when they're editing some rich text), for which we'd ideally be able to show what the font looks like when they're selecting it from a ComboBox or ListBox.