New maps, units, scenarios are already being produced. You can turn Germany back into it's early 1940's or summon a god made out of spaghetti and meatballs. That's just the start of the options you will have at your disposal. You will have to purchase the game to get in on the action. Using the mods obviously requires the game, but to make them will also require the purchase.
There is also a few more new game entries to the Workshop as well. Dungeons of Dreadmore and Naval War: Arctic Circle are now ready for you to mess about in their games too. You might be curious to know that D of D is also free to play and NW:AC has a free demo too to get you started.