I think improving mod-ability is the most important part, there is no way in hell they can compete with modders in terms of content or that perfect balance for everyone, instead they should create the tools for the community(paradox games like HOI etc are a good example for that).
personally, I dont want to see diversity, other than the required eye candy for the good reviews I want more work done under the hood, finish the transportation system, add more customization options, fix bugs, improve stability(thou I never had any problems with it), improve performance which will allow better economical models and algorithms, keeping mod computability and obviously better modding tools. because the more tools/options we have the better the game will be see SC4 amazing moding resources.