Announcement from Sia team :

Bitmain has announced ASICs for Sia, shipping in 7 days. 1275w, 815 GH/s, ~$3200 USD. They are more expensive and less efficient than the Obelisk SC1, but they ship several months sooner (7 days as opposed to several months).

Bitmain has a long history of being abusive towards coin communities, their customers, and towards coin developers.We prepared for something like this by adding an extra feature to the SC1. We can do a soft-fork that slightly changes the PoW algorithm which would invalidate the bitmain ASICs, but allow the SC1 units to continue working. In the event of an attack from Bitmain, we can activate this soft fork. At this time, I do not think it is necessary, but if they start mining empty blocks or otherwise prove problematic for the network, we have recourse that does not involve destroying the usefulness of the SC1 units. This fork would of course require community adoption, it's not something the devs could decide to activate on their own. It would be a UASF, because the majority hashrate would not be standing behind the soft fork.

Overall, I do not think we have much to worry about. Hopefully (and very likely), this soft-fork will never be necessary. But I wanted to remind everyone (including Bitmain) that, at the end of the day, it is the community that has control, not the miners. If ASIC manufacturers act in a way that is harmful to the network, we have recourse.