Official Civilization 6 mod tools and Steam Workshop integration aren't ready yet, but they are still on their way. Firaxis's Pete Murray reconfirmed during a multiplayer livestream today that "the team is working on those, and when we have more information to share with you, we will be sure to do so." You can watch the statement in the Twitch clip above, posted to Reddit by user ConsiderableNames.
Murray also included multiplayer teams in that list, which is another hotly requested item among the multiplayer community. We had previously heard these features were coming, but Firaxis hadn't given too much information recently about the status of them. So in this case, no news is good news as it means nothing was canceled.
Of course, the lack of official mod support hasn't stopped people from making great Civilization 6 mods, but the community hasn't grown in the way Firaxis's other hit XCOM 2's mod scene did by having mod and workshop support at launch. Obviously they are different teams working on the two games, but given the lush history of Civilization 5 mods one would think support would have arrived sooner. Still, it's always nice to see big developers support the mod community at all.