I am happy to see this coming to Steam, that's a big positive! The exposure alone will boost sales immensely.
My concerns will be the problems City Skylines had with their workshop which was the lack of proper organization (proper tagging and enough sub-menus) and creating a proper image for each asset. I'm sure this is being worked out since everything has been stellar so far with this game, but i'd love the ease of use to be much better than we dealt with trying to find good assets with CS. Hopefully there is an exporter in the game that gives you all the tags and options and control over these things.
As for everyone complaining about having a limited access account. My sympathy is slightly low. The cost of PC (at release) is fairly low for game of this caliber, Steam itself is free, so all you'd have to do is spend $5 towards steam to unlock the full account... which by this point you've still spent less than most games cost at base price. But even if you have a limited account you still have access to downloading custom assets and blueprints which is what 90% of you will be doing. Those of you wanting to upload and add to the database and haven't ever used Steam before... that really small minority may have to invest an extra $5... which is very little overall. If that $5 is breaking the bank for you, then maybe sitting around and playing games all day isn't the right corse of action in your life right now.