After a period of testing, Linux support is now available.
Additionally, Workshop support is currently in beta testing, and will be fully available soon. If you'd like to join the beta, you'll need to opt-in via the game's properties, and also join the Workshop beta group to gain access to the Workshop community page:
http://steamcommunity.com/groups/rts_workshop
Keep an eye out for the Workshop announcement in the next few weeks - we're planning a big level creation contest!