I've started making my own maps, it's lots of fun...but I agree with Cruxador, if you're going to break this long held tradition of no DLC, and instead giving paying customers extra content, wit occasional paid for expansion packs... a map pack is really not the way to go for your first DLC.
Please bear in mind that there is still a good amount of content I haven't seen, so if I mention something that is already in the game, excuse me.
I'd like to see the war between man and fallen be more emphasized, there doesn't seem to be too much in the way of gameplay mechanics here.
It would be awesome if we could get a Unit Designer in the workshop, so we could design units for the A.I. to use as our opponents, as it is now you actually have to play as that race and get to the proper tech level to design the units, this would be a welcome addition that would really add a sense of life the opponents
I definitely think there should be more items, both as loot in the world and to research as troop equipment. Especially trinkets and accessories like +X Exp Rings or +Y% Crit Chance, Rings of Regeneration. I'd like to see more poisons tied to the Assassins Tools faction trait. Poisons that have differing effects, not just more powerful D.O.T.
I'd like to see the ability to create your own magic items, Either through a Sovereign Trait, or perhaps a semi-advanced tech on the magic tree.
I'd like to see the ability to set what type of land is created in your zone of control. For example, my land could turn into swamps, of course different land types would cost varying faction trait points. I know this idea is a bit out there and I'm not likely to see it implemented, I'm just trying to illustrate the point that there is so much awesome stuff that could be done with this game, I'm exciting to see new ideas.