However, with more of the coin will in circulation, what impact will this have on SIA price?
None to little. The daily Block Reward will stay the same but mostly distributed between Obelisk owners.
Nobody can accurately predict what impact these ASICs will have on the price of Siacoin, BUT I CAN give you my rosy speculation if you're interested...
Crypto is such a new asset class, it's hard to find precedent / correlaries... That being said, if you look at the trading patterns of Litecoin and Dash after their first asics hit the market, I believe you'll find that the price initially dropped. I asssume a lot of that was miners looking to ROI by converting to btc or cash, but who know?
That was in the short term... had those miners HELD ON TO what they mined, even when the price dropped, they'd probably be millionairs now, or close to it... In other words, if you factor in the giant price increase of ltc/dash, those first gen asics were EXTREMELY profitable, in spite of the initial dip in price.
That's not to say that will happen here... 2 alt coins are a very small sample set
There's also a big difference between the Obelisks and those first generation ltc/dash Asics...The companies that built the first litecoin and dash asics did so because they thought it would be profitable... they thought it would be profitable because the price/profitability/interest in the coin was already present.
Those factors probably/definitely could/do have a lot more to do with the meteoric rise in price litecoin and dash have enjoyed. The Obelisk Asic company, on the other hand, is comprised of the same developers ass the coin itself... They CHOSE to build an Asic for Blake2b, not because they thought it was the most profitable algo to mine, but rather to add security to their network.
I do think that having a more secure network, AND a development team capable of getting an Asic to market is indicative of a coin that's going places, but nobody knows. It's uncharted territory.. They haven't even done it yet...
But if I may make one humble prediction, I think that future mining newbies will do a quick search for what alt coins can be mined with Asics, and (with the oversaturation of other algos) seek out an Obelisk if only for the novelty and diversity.
TLDR: While having an Asic doesn't guarantee any rise in price for a coin, I do think it's a good sign and indicative of a stable coin with a future. The success of the coin will ultimately hinge on whether people use their coin for decentralized data storage... But an asic is rarified air for sure, and great first step.