I think it would be awesome to be able to increase the default polycount for the character. For example, when I import characters in UE4, the close-up body seems a bit blocky due to the lack of polygons, although they look great in CC3 due to the subdivision function, but the exported characters do not inherit it. This can be fixed in UE4 by enabling the tessellation feature in the material, but the solution is not perfect (see why - https://forum.reallusion.com/410267/Tessellation-issue-in-Unreal-Engine).
Also, it will add a lot more freedom to the GoZ feature if we'll be able to work with a more detailed model in ZBrush - even the highly deformed characters will look great with this feature. In my opinion, it will be specifically useful for film & tv productions where you don't really care about optimization but you need to achieve the best look possible.