"If you've been following our Update Roadmap, you'll know that Tarn has been busy prioritizing Steam Workshop integration," says the latest developer update over on Steam. "We are happy to announce that indeed Steam Workshop will be available at launch. This means that you'll be able to find and install Dwarf Fortress mods with ease."
Modding has always been a big part of Dwarf Fortress, although most often those mods are adding tilesets, UI tweaks or world visualisers to make the hugely complex simulation more legible. Dwarf Fortress's Steam release already does most of those things itself, with an official tileset, a mouse-driven UI and proper tutorialisation. In any case, there remains enormous modding potential in a game as rich as Dwarf Fortress.
The post does also explain that the focus on getting Workshop support ready means that Classic and Arena modes won't be included at launch. Arena mode is where you can spawn Dwarf Fortress's various monsters and watch them fight and although fun, it's far from essential. Classic mode, meanwhile, lets you strip Dwarf Fortress's Steam version back to its original ASCII graphics while also keeping ASCII-only versions of the Steam release's new UI.
Finally, the post mentions that official Dwarf Fortress merch is on the way, including a pin, a metal-band style t-shirt, and a pint glass. I'm not much of a merch guy but the t-shirt is cool.