Official response from the SIA [SC] Dev Team
"Bitmain has announced an ASIC miner for Sia. This has made a lot of people uneasy, especially those who preordered Obelisk units. So I'll first address the Obelisk units in isolation. Though we don't have the full chips back yet, the chips are in production and we have our final simulations. We can confidently state that the bitmain unit is far less energy efficient, costs more money, and is an objectively worse miner than the SC1. So people who ordered Obelisk units will still be receiving hardware of substantial value.
As a developer, Bitmain moving into the Sia space makes me uneasy. Bitmain has historically been extremely greedy, and very willing to sacrifice the well being of the community, of their customers, and of the ecosystem if it means they can make a couple of extra dollars. The biggest way this has manifested for altcoins is that they will over-sell hardware. When a ton of miners suddenly join the network, the difficulty adjusts. If too many miners join the network, nobody is able to make any money, and everyone eats a loss on their hardware purchase.
Bitmain has no qualms about overselling their units to buyers. They take massive margins on their hardware (>50%) and make more money than the total block reward at the expense of their customers. They over-saturate the mining market in a way that hurts their buyers. I think we will see this with Sia. Bitmain will sell more units than the Sia ecosystem can sustain, and many people end up with large losses. Bitmain will not end up with losses, because they were paid up-front with non-refundable money.
Bitmain also has a history of doing things like mining empty blocks, and like refusing to activate soft-forks that are beneficial to the network. They were openly hostile to the Bhttps://bitcointalk.org/index.php?topic=2769785.120itcoin-core developers, and actively blocked the activation of a very valuable network feature (Segwit).
We, the dev team, are not happy that Bitmain has made an ASIC for Sia. We are not happy that many Sia supporters are at risk of losing money by buying these miners (from over-saturation), and we are not happy that Bitmain may choose to interfere with our network. This is not a commentary on general ASIC companies, this is a commentary on Bitmain specifically.
We did add an extra feature to the SC1 unit that would allow us to invalidate the Bitmain hardware without invalidating the SC1. The community would need to choose to adopt a soft-fork (it's not something we could just magically activate, we have to change the hashing algorithm slightly), and then we could get rid of this cycle of Bitmain hardware. Of course, they could just create another round of hardware (likely taking ~3 months). And, it would hurt Bitmain customers more than it would hurt Bitmain. Bitmain has already sold around $20 million of non-refundable hardware. They have made their profit, and a soft-fork wouldn't change that.
As much as I would like to punch Bitmain in the nose, I don't think a soft-fork achieves what we want. If the hardware is used to harm the Sia network, either by doing double spends, rejecting soft forks, mining empty blocks, we will invalidate it without hesitation. But for the time being, I think the best thing to do is to advise people not to buy the Bitmain hardware (to protect yourself from the oversaturation that Bitmain tries to create), and then to watch and wait, and respond more if it appears that the network is under attack. Overall though, I do not think Sia is in trouble.
I am looking forward to the thoughts from the community."
https://www.youtube.com/watch?v=f4bxnepOcyM
I knew that they sold 6K miners in Chinese mainland. 
