I don't understand what you're problem is with Blockland being able to use Steam Workshop. If anything, it will just be another place to upload and download Add-Ons. We might even get official, optional/non-default Add-Ons like Cog's Click Challenge Gamemode and that script that only allows you to build on baseplates connected to eachother.
I don't know about you guys, but I love it when Badspot posts a non-default Add-On that he made. Blockland getting on Steam, and maybe even using Steam Workshop would be nice.
Getting Blockland on steam means more users, more servers, more players in your server, more add-ons, and more updates.
I like how the "more add-ons" and "more updates" are separated. Maybe we could get official non-default Add-Ons. A free DLC type thing. Kind of like what Valve does with their games, except optional.