attributes (sounds).
When you state sound, are you referring to the function of changing a squad's sound set in the mod tools, the speech codes?
Anyway, besides all those you listed, here's wishing that the feature of importing custom sounds into mods (just like custom models and animation) will also be added in the future. Currently though, it's a good thing we can at least import custom images for unit portraits, abilities, etc.
Also, I feel that, with a stronger set of modding tools, the modding community will be more motivated and inspired to create full-fledged total conversions, even to the extend of venturing into creating mods representing fictional, and original universes. EDIT: The gameplay style of Company of Heroes is great for these kind of things.