There are a few features in the current type style editor that would be very welcome additions.
Override styles without losing the connection to the style definition.
It is obnoxious needing to create a different style for each variation instead of maintaining the same attributes unless overridden. If I underline text, it will maintain the connection to the primary style and receive any later adjustments to the style. The underline will persist unless the style is reset, similar to how overrides in a component are handled.
Type style inheritance.
I have found myself wanting to update the typeface for a variety of type styles. This would also be helpful with any other attribute of the style. If there was an inheritance model that could be modified, that would make the experience of managing type styles much easier.