If the game had something like a racial talent tree it would give Blizzard the option to get more nuanced with racial abilities. It shouldn't have the complexity of the current new talents or scale. Something that is a blend of the new talent system, earning points every so many levels, and the Netherlight Crucible in terms of scale and having rows with choice options. Also getting some new racial talents that are thematic when a new expansion drops could also allow the system to expand and grow.
I know some people probably won't care about this, but it could add some additional way to personalize your character at a more core fundamental level and could bring back some of the older racial abilities that were removed or come up with a bunch of new fun ones people can play around with.